If I am referring to one thing, but multiple people, is it "is this _ one of yours?" or "one of you all's"?
- Anybody can ask a question
- Anybody can answer
- The best answers are voted up and rise to the top
would be how I would phrase the question. Though some dialects of English commonly use
If you must use either of your two examples, use the first:
The problem is ambiguity: are you asking whether this table belongs to "one of you," or whether this table is one of several that belong to "you"? Presumably it would be obvious from the context.
It would be better by far to avoid that construction altogether and say,
"his book": one person owns one book
"his books": one person owns many books
"their book": many people own one book
"their books" many people own many books
Side note: It's too bad that "yall" is not the accepted plural of "you", it could eliminate ambiguity. I am reminded of a book on language I read once where the author commented that when he was in college, he asked his girlfriend to go away with him for the weekend. But at the time he asked she was with a group of her friends, and when he said "you" they thought he meant you-plural, and that he was inviting the whole gang to go on a trip. Caught in an awkward social moment he felt he couldn't clarify his meaning, so what he had intended to be a romantic getaway for two instead became a road trip with a bunch of strangers. He said he considered that an "unacceptable ambiguity".