I notice a lot of Seventh Day Adventists and JWs on OKP when I do these. It's certainly a different perspective than anything in the circles I run into, so I appreciate those questions. But go ahead and ask away, whether you're a Bible-only Christian, a Catholic yourself, an atheist, or what have you.
Can be about the faith, practices, timely news stuff, or good old fashioned apologetics-type of questions.