CNN will be taking questions from social media with the hashtag #CNNDebate. You can tweet now or at any time during the debate tonight.
I personally don't tweet, struggle to keep up with email, blogs, and print media.
But I suggest asking questions such as
"NAS, other major science academies warn that burning fossil fuels threatens more extreme weather. You are "not a scientist" but what if they are right?"
"Do you support shutting down the government unless Planned Parenthood is defunded, although no public funds go to abortion?" Pick your own top topics - a good source of ideas IMO is Bernie's 12 point economic justice program and his racial justice program, but you can pick any popular issue on which they are on the wrong side.