Is Dominate Person's telepathic link one-way or two-way?

Question

Does Dominate Person form a one-way or two-way telepathic link?

If the link is two-way, can the target communicate (willingly or when asked) information? Does the target need to spend a turn or bonus action when using this link? Does the caster perceive what the target perceives like Find Familiar spell?

Possible uses I'm thinking of is to form telepathic link with characters going to search separate rooms, or send the dominated person to investigate an area. (The range of the link is not the scope of the question, but would be nice to have.)

Answer 1

One-way telepathic link only

Dominate person's telepathic link is only used for issuing commands to it not for communication

In 5e, spells only do what they specifically allow you to do, nothing more or less. And the way the spell is written only allows for a couple specific uses of the telepathic link described in it.

Dominate person gives you a telepathic link to the dominated creature that you can use to issue commands to it which it then does its best to obey.

While the target is charmed, you have a telepathic link with it as long as the two of you are on the same plane of existence. You can use this telepathic link to issue commands to the creature while you are conscious (no action required), which it does its best to obey.

The spell then proceeds to describe how this telepathic link can be used to issue commands to control the creature in either a broad or a specific way.

Nowhere in the description does it say that any other kinds of communication can take place through that telepathic link. Only that the link is created and that it is used for issuing commands. And, if the spell does not specifically give you an ability, then you do not get that ability.

Jeremy Crawford has specifically ruled on similar cases several times (here, here, and here for example) and each time the answer says that the ability must say that the creature is able to respond or else they cannot.

In the end, the purpose of dominate person is to control a creature, not to talk with it.

Spells that allow communication specifically say it and outline the rules for it

For example, find familiar says:

While your familiar is within 100 feet of you, you can communicate with it telepathically.

Note that the wording is different between the two: dominate person says "you have a telepathic link with it" whereas find familiar says "communicate with it telepathically". Communicate makes it perfectly clear that the telepathic bond is used for communication. It then proceeds to outline how that works:

Additionally, as an action, you can see through your familiar's eyes and hear what it hears until the start of your next turn, gaining the benefits of any special senses that the familiar has. During this time, you are deaf and blind with regard to your own senses.

Note that this is a major and relatively unique feature of the find familiar spell to be able to see through the familiar's senses and it comes with rules and consequences. If the designers wanted to have this be part of the dominate person spell they would have HAD to have added some rules to explain how it works. This is much too major a point to have just overlooked since it changes the spell entirely. Thus, it seems they did not intend for the spell to work that way.

This makes complete sense because the link created by dominate person is not for communicating, but only for issuing commands. On the other hand, find familiar is specifically enabling for two-way communication between caster and familiar.

Jeremy Crawford has also supported the idea that telepathic abilities can be one or two way:

Some abilities allow sending thoughts, some allow reading thoughts, and some allow both.

If you want to communicate telepathically, you have to use telepathy (or something like it)

Telepathy says:

You create a telepathic link between yourself and a willing creature with which you are familiar...Until the spell ends, you and the target can instantaneously share words, images, sounds, and other sensory messages with one another through the link

It is important to note, that without the above text, the spell would do nothing. A telepathic link without a description as to what the link does is useless. Clearly, though, telepathy is intended to be used to allow two creatures to communicate mind-to-mind and so it describes how that works and the rules associated with it. As discussed above, dominate person's purpose is different and thus it is described differently. Since dominate person doesn't have any of this kind of text it is clear that the telepathic link described therein is different and not intended to be used the same way.

Your specific questions:

• If the link is two-way, can the target communicate (willingly or when asked) information?

  No the communication is not two-way. No information can be exchanged. The ability to communicate is something that would have to be written into the spell (and is for other spells). Also, this interpretation would make dominate person much more powerful then higher level spells which makes no sense.

• Does the target need to spend a turn or bonus action when using this link?

  Target cannot use the link (see above).

• Does the caster perceive what the target perceive like Find Familiar spell?

  No, that effect is specific to find familiar and there is no similar language in dominate person.

Answer 2

Something in between

Let's analyze Dominate Person:

You attempt to beguile a humanoid that you can see within range. It must succeed on a Wisdom saving throw or be Charmed by you for the Duration. [...] While the target is Charmed, you have a telepathic link with it as long as the two of you are on the same plane of existence. You can use this telepathic link to issue commands to the creature while you are conscious (no action required), which it does its best to obey.

So the link works for what it works, to issue commands. In D&D 5e a spell does not do anything it doesn't say it does, and since "telepathic link" is not (AFAIK) a term that implies two-way communication, there is no two-way communication. However:

You can use your action to take total and precise control of the target. Until the end of your next turn, the creature takes only the actions you choose, and doesn't do anything that you don't allow it to do. During this time you can also cause the creature to use a reaction, but this requires you to use your own reaction as well.

This is a bit tricky, since it's not clear whether "total and precise control" means you can perceive what the subject perceives. Since you could use any of the subjects class features (other spells and effects that do not let you explicitally state so) I personally would rule that you can perceive what the target perceives, or the "take full control" would be pretty much useless without line of sight, and even then tricky.

For example, let's imagine you are 20 yards away from a dominated creature, and you want to take full control to attack some other creature. If you can't know how much pressure you are applying to the sword your dominated creature is wielding, and you can't accurately judge the distance between your dominated creature and its target from your position, even scoring a hit would be really hard to do. And of course, if you have no line of sight and you don't get the sensory information from your dominated creature even taking a step would be hard, since you wouldn't even be able to know if your dominated creature is standing.

Alternatively, one could think that "full and precise control" means you can "micromanage" your creature movements but it's still said creature who is doing them. It would still be pretty much impossible to fight without line of sight (how would you know when to use a reaction?) but more "relaxed" activities, like writing a letter, could be possible. Still, in this case it would seem that using your action for taking "full and precise control" without line of sight is pretty much useless, since you can only effectively use it for thing where a normal verbal command would work just as well. Also, to me this case doesn't really sound as "full and precise control", but that's just my opinion.

Without sage advice or some other factor to clearly state which of the two cases is correct I'm unable to provide a definitive answer, but I would personally rule that "full and precise control" includes sensory information as long as no info contradicts this.

In conclusion:

The link works for two purposes, to issue commands (no action required) and to take full control (action required). When taking full control one could arguably perceive what the target perceives. In any case, the link does not allow the subject to communicate with the caster, so barring some creative use of "taking control" or asking the subject to employ a feature allowing distant communication (a spell like sending, for example), he can't. And finally, the range is is "same plane of existence".

Answer 3

The wording is separated by a period. This means that you have a telepathic bond/link and in the absence of rules countermanding English language usage, English prevails.

Telepathic: supposedly capable of transmitting thoughts to other people and of knowing their thoughts; psychic:

Obviously, in real life the "supposedly" is used since it yet to be empirically proven. According to this definition there is no mention of sensory information, however, if the dominated individual were to think that something is hot or cold etc. the caster could pick up on that. In essence the target only need think about things and that would be communicated to the caster. This could be complicated and the DM may make you expend an action of some sort to process a lot of data if he/she deems fit.

While the target is Charmed, you have a telepathic link with it as long as the two of you are on the same plane of existence.

Through that link you are able to send commands that they must obey to the best of their ability assuming they are on the same plane of existence as you.

You can use this telepathic link to issue commands to the creature while you are conscious (no action required), which it does its best to obey.

When taking "complete and precise control" of the target you should have sensory access otherwise you can't have "precise" control of something.

There is some discrepancy with Awakened Mind as being intended as only one-way communication though. But that is a specific ability and not a general ruling about all telepathic abilities in the game.