What's a proper but simple one-word description of a person to whom a question is being asked?
Addressee is the usual technical term for anyone being talked to, without regard to whether the talking involves a question, a statement, an order, a promise, or whatever. I don't know of any that specifically refer to questions, though.
Questionee and interrogatee are grotesque hapax legomena that call attention to themselves, and to the pomposity of their user. Use the person's name instead, if you know it, or find a more comfortable term to refer to them with.
Merriam-Webster has questionee:
one that is questioned
Though these are uncommon words, I believe their meanings are clear enough for them to be useful in apt circumstances.
I'd prefer a word like respondent, though, if the questionee actually responds.