I use Tor a lot. Is it OK to use Stack Exchange sites in Tor? Can I use Tor to access, answer or ask questions on Stack Exchange?
Is it against any rules here on Stack Exchange? If so does it affect my reputation?
Using TOR to post on SE is perfectly fine, there's no rule against it at all.
If you're using a low-rep account, odds are you'll be frustrated by the experience though. You're not the only one using TOR, it's pretty popular with people that commit vote fraud or abuse SE in some other way. There are mechanisms against this kind of abuse, and those will block any user of the same TOR exit node if they're triggered.
Having high reputation, I think at least 125 is the threshold, will avoid most of those anti-abuse mechanisms.
And just to be complete, using TOR to avoid any limits or break any rules on SE won't help you much. Using it for anonymity is fine, using it to hide multiple accounts from the moderators and break the rules is not.