One of the great pedagogical questions is "How can I engage students with material they are not interested in?" This is never more important than in the case of Bible classes, where we want non-Christian students to participate in a meaningful manner.
There are various aspects to getting students to ask questions. Two important considerations in Bible class are anonymity and the freedom to ask literally anything. By having anonymous methods of asking questions, students feel they can ask "silly" questions or, more importantly, questions they think are offensive - even questions they know are offensive and designed to attack the Christian faith.
Today we took the opportunity to have a Q&A session for part of the lesson and I made sure students knew it was anonymous, and that they could ask anything even if it was offensive. I did say that I reserved the right to re-phrase some questions to be suitable for class discussion.
Some students took the opportunity to ask really ridiculous questions, but I noted some students (who are usually disinterested/disengaged participants) watching each person who spoke with great interest. We usually explore the question more fully before trying to answer it, and the discussion of even the other students was more animated than usual.
We can't do lessons like that every time, but it is my hope that the occasional session like this will build a "habit of participation". If non-Christians can engage in lessons more, that is a step closer to them engaging with the Gospel of Salvation.