I think that would have an individual answer; some Ts might not discuss some things and some clients not other things, etc., I believe one has to ask to find out where the boundaries are and decide what one thinks about them, they aren't "obvious". If my T asked me something I did not want to answer, I would not answer :-) If I thought it was inappropriate or something, I'd ask why it was important or they'd asked it, etc. Since therapy is about the client, I assume a lot of therapists would not answer personal questions about themselves, their lives but it would not be wrong, bad, etc. to ask them, but, for me, the same condition would apply, what does it have to do with me and my therapy. I would not ask any question of anyone that did not have some basis other than my nosiness