As a wizard, I cast spells and such, then die. I have a clone set up in my demiplane (created using the clone spell; granted, I don't know any other ways to create a clone).
When I "wake up" my clone's body, do I have all my expended spell slots back?
First of all, the clone is considered a distinct creature from the original, based on these passages from the description of the clone spell:
This spell grows an inert duplicate of a living, Medium creature as a safeguard against death. [...]
At any time after the clone matures, if the original creature dies, its soul transfers to the clone, provided that the soul is free and willing to return. The clone is physically identical to the original and has the same personality, memories, and abilities, but none of the original's equipment. [...]
Being a distinct creature means, among other things, that the clone has its own spell slots distinct from the original creature. So expending your spell slots prior to dying will not expend your clone's spell slots. The remaining issue, then, is the "initial state" the clone's spell slots. For this, we need to look to these passages from the description of spell slots in the Spellcasting chapter:
Regardless of how many spells a caster knows or prepares, he or she can cast only a limited number of spells before resting. Manipulating the fabric of magic and channeling its energy into even a simple spell is physically and mentally taxing, and higher-level spells are even more so. Thus, each spellcasting class's description (except that of the warlock) includes a table showing how many spell slots of each spell level a character can use at each character level. [...]
When a character casts a spell, he or she expends a slot of that spell's level or higher, effectively "filling" a slot with the spell. [...]
Finishing a long rest restores any expended spell slots.
From this, we can see that each spell slot generally represents the ability to cast one spell of that level per long rest (or per short rest, for warlocks). As with all other class, racial, and other features, this ability is inherited by the clone. Since the clone has never cast any spells prior to waking up, none of its spell slots are expended when it wakes up.
(As indirect evidence, this interpretation of spell slots is consistent with the wording used for many other once-per-rest features, which generally say something like "You can do X. You regain the ability to do so when you finish a long rest." Such abilities would also start out ready to use for a newly-awakened clone.)
Assuming this clone was created by the Clone spell, the spell description states (emphasis added):
At any time after the clone matures, if the original creature dies, its soul transfers to the clone, provided that the soul is free and willing to return. The clone is physically identical to the original and has the same personality, memories, and abilities, but none of the original's equipment.
This implies that abilities and related things are tied to the soul, rather than the body—for instance, you still have any new abilities, levels, new total spell slots (which may or may not be available before a long rest), etc. that you've gained since the clone of the body was created. Since the original wouldn't have had the ability to use those expended spell slots, neither does the clone.
A well-regarded answer on a related question espouses this same principle for why a Cloned character does not regain the ability to cast Wish: spell-casting abilities are tied to the soul, not the physical body.
For the sake of context, let's imagine that a 17th level Wizard casts the Clone spell, targeting themselves. Then years later (say they are now level 20), they enter into an epic battle as part of a war. They fight valiently, but run completely out of spell slots on the field. They fight with cantrips for a time, but eventually the swords and axes of their enemies are too much, and they drop. They are attacked while dying several times, forcing failed death saving throws, and they die.
What happens next? Will the clone that awakens have its spell slots restored, or not?
Well, before we go any further, let's establish one important detail:
In the above example, we have a 17th level wizard who clones himself, but then is 20th level when he dies. So which version is the clone spell meant to emulate? The 17th level one, or the 20th level one?
Here, the text of the spell (bold added) can give us some guidance:
if the original creature dies, its soul transfers to the clone, provided that the soul is free and willing to return. The clone is physically identical to the original... The original creature's physical remains, if they still exist, become inert and can't thereafter be restored to life...
In this text, we see that "the original" refers to the creature that dies, and left behind remains. And that the clone is identical to "the original." No 17th level wizard died and left behind remains: a 20th level wizard did. What the wizard used to be (e.g. 17th level, 18th level, a toddler) is not what the spell is reproducing, but rather the creature that just died. So we can safely say that the creature created by the clone spell is to be compared to the original creature at the time of death.
(I know that was a weird segue: trust me, it will be useful later).
As always, it's worth looking to the text of the Clone spell first, the most relevant section of which is probably this one:
The clone is physically identical to the original and has the same personality, memories, and abilities, but none of the original's equipment.
This statement gives us some guidance, but it's open-to-interpretation at best. Does a spell slot count as an ability? Memories? Personality? Equipment? Some of these categories are more viable than others (i.e. existing answers have tried to categorize a spell slot, or a lack of a spell slot, as an Ability), but none are ideal.
One thing we can say with certainty is that spell slots are a resource: one that recharges under certain circumstances, like a long rest, and allows a creature to do certain things while they have them. So...
Again, the rules here are unclear.
You could make an argument saying that a target's spell slots being considered as a resource means the Wizard loses the spell slots: perhaps pointing out that equipment is also a resource of a kind, and that the clone has "none of the original's equipment." But I put it to you that such an argument is doomed to failure for one simple reason:
hit points.
Hit points are also a resource in this game. Like spell slots, they determine which of your abilities you can use, and which you cannot (for example, a high level Monk could still use their Diamond Soul ability at 0 hp). Like spell slots, they recharge on a long rest. And like spell slots, the wizard in our hypothetical example was entirely out of them when he died.
Now, of course there are differences between hit points and spell slots (for example, whether or not all characters have them), but the essential point I see here is this: if the argument for spell slots being restored or left as they were when the original creature died is because their presence or absence defines the characters' "abilities," then the argument is equally true for hit points, which also define a creatures' abilities by their presence or absence.
And as we've established, the cloned Wizard is copied based on their original at the time of its death, not from some earlier version. As such, it is very likely to have zero hp when it died.
The spell gives some guidance about resources connected to the creature's survivability, but this guidance is similarly unclear, or even contradictory. (e.g. that the spell is "a safeguard against death" implies the hit points return, but the fact that the copy is "phyiscally identical to the original" at the time of death implies they do not). Ultimately, the DM will have to make their own decision.
Now, the DM could come to conclusions other than restoring all of both, like declaring that the clone awakens with 0hp and no spell slots, but is stable. But the clone spell heavily implies that the cloned creature should awaken when the original creature's soul enters its body. Note that one of the options for the clone's container is a "mud- filled cyst in the ground, or crystal container filled with salt water." In short, some of the options for the container would be deadly to a breathing creature who was unconscious when they returned to life, which defeats most of the point of the spell.
As such, if a DM wants their rulings to be logically consistent, they likely will have to conclude that a Clone will have its spell slots restored if they want to have the clone's hit points similarly restored.
Well...
The above relies on a DM needing to have their arguments be logically consistent. And the simple truth is, that's not something they're bound to. A DM will make the decision that makes the most sense to them, or that seems like the most fun. So they could definitely conclude that hit points and spell slots are to be treated differently by this spell, just because (Alan Mills makes an interesting point in their answer about how fully restoring spell slots could cause balance issues, for example).
However, without being able to know your DM's decision (which can override any explicitly written rule anyway), we will give advice on this site as best we can based on existing resources available to us, some of which are the rules and logic. And if we want these rules to be applied in a logically consistent way, then if hit points are restored by the Clone spell (and they almost certainly are), then spell slots will be similarly restored.
The clone spell description starts with the following sentence:
This spell grows an inert duplicate of a living creature as a safeguard against death.
If the clone were an entirely new creature, then this sentence would make no sense. The clone spell is a get out of death method for certain spellcasters which lets them immediately revive if their current body dies. Their soul moves into the new body and they get all of the memories, abilities, etc. that they had when they died. However, since they are still the same being, the rules on regaining spell slots still apply and they don't regain any expended spell slots.
Allowing them to do so would offer some overbalancing character options. Provided they had the resources, they could create an army of clones. Then, when they ran out of spell slots, they could commit suicide, reawaken as a fully prepared clone, and teleport straight back into the action repeatedly.
I am assuming you are talking about the result of a clone spell here. The description states that it produces
duplicate of a living creature
and
The clone is physically identical to the original and has the same Personality, memories, and Abilities, but none of the original's Equipment.
Now, nothing of that is talking about mental "resources" or even illnesses (which a missing spell slot could bethought of at kinda). Or even what the "duplicate" refers to.
In my opinion, you get the spellslots you had when originally casting clone, because that is when the duplicate was created. Given a lack of specification, I just assume a perfect duplicate.
On the other hand, it should not matter: you are safe in a demiplane, where you should have stashed food and a bedroll anyway. Just take that long rest.
Your real question is actually this: Are spellslots bound to the body or the soul? Another fine question where we don't have an answer either sadly. But maybe with this phrasing your DM can rule a more intuitive answer (like some sorcerers regain all of them or none depending on their origin/bloodline, warlocks none [because their source of spell slots is a deal made about their soul], wizards maybe a few because their now rested body can focus a bit better etc.
