Could you replicate a single spell known (a wizard with a single spell in his book)?
You cannot. Because "ability to cast a specific spell" is not one of wizard's class abilities. They have the ability to cast arcane spells, and any item requiring you to be able to cast arcane spells can be tricked using UMD.
If the requirement is "able to cast Fireball", then all you have to do is to emulate that you are a 5th level wizard (a DC 25 check), which are all able to cast Fireball, and you would trick the item just fine.
Could you replicate domains/bloodlines/mysteries for a small pool of spells known
You can trick the item saying that you are a Rakshasa Sorcerer, or Conjurer Wizard, or a Cleric with the Fire Domain, or even that you have a certain archetype such as Hexblade Magus. You may also trick the item saying that you do have a list of Spells Known. And any spell added from a bloodline, domain, mystery, or similar class feature, is automatically added to your class's spell list, as noted by Sean K. Reynolds (ex-developer).
But you may not trick the item into saying that you known Fireball because that's not a class feature of those classes.
Could you replicate all wizard spells by replicating a wizard with a full book?
No, owning a spell book, or requiring one to cast spells is not a class feature. It is a limitation on preparing spells imposed on wizards, witches (through their familiar) and arcanists. But not a class ability per se. If the item asks for a "prepared caster" or "cast spells like a wizard", then you may emulate that ability by saying you are a wizard (Harry).
What abilities are there (like spell blending) to replicate that could give you a single spell?
If a class has the ability to cast a specific spell, then you may emulate that class ability. But as noted by James Jacobs (Creative Director) before, UMD does not let you use that class ability, you simply bypass the item's requirement for that ability:
Over at the PFS section there is some confusion on how the UMD Skill works in regards to emulating a class. The question was targeted at Ring of Revelation. The argument is can a non-oracle utilize the ring to gain temporary access to a revelation with a sufficient roll of UMD? Some argue that no, you have to be an Oracle, and if you're not UMD won't help you. Others say that UMD circumvents those standard preventions.
Use Magic Device will let you trick an item into thinking you're a different class... but it does not grant the POWERS of that class. The way the ring of revelation is worded pretty much means you HAVE to be an Oracle (aka you have to meet minimum level requirements in class abilities granted by the oracle class, since the powers granted directly affect that ability rather than grant you NEW abilities). Furthermore, the ring specifically says that it has no effect if worn by a non-oracle.
So. Best case scenario, you could Use Magic Device to trick the ring into activating, but if you don't actually have class levels in oracle, the ring will do nothing more than take up a ring slot for you.
Which is also noted on the description of UMD:
This skill does not let you actually use the class feature of another class.
What is important to keep in mind here is that you do not replicate class abilities, you trick the item into thinking that you are a member of that class, or that you have that class ability, which is better worded as emulate, instead of replicate.
You may cast whatever spell is on the scroll (using UMD), and you may even scribe a scroll later on it (since it is still a Caster's Shield), but it won't wont randomly replace the spell cast on the scroll unless you are actually a caster, since you don't actually know any spells and that's not a requirement to use the shield, it's part of the shield's effect.