Molly Pennington, PhD, PhD, Former Professor, Writer
Class discussions can be nerve-racking when everyone is sitting in silence. Is the question too hard or is it just that no one did the reading? I understand that you might want to break the ice, but you should definitely sit this one out if you aren't familiar with the topic or assignment--unless you're willing to bring that up as part of your comment or question.
For instance, would it be useful to say something like, "I found it difficult to get past the first pages of the assignment. I didn't understand what the author meant in this passage." Then give an example. While you won't score any points for not finishing the reading, there's a good chance that other students may be just as confused. And your professor will probably be open to explaining and breaking down the reading if students found the concepts hard or confusing.
Questions like this can be a good way to get discussion started and to keep it substantive.
Asking "obvious" questions is not a productive mode, unless you have follow-ups that can lead the discussion in more fruitful directions--which you don't if you haven't done the reading.
I know that some readings will be missed due to various circumstances, but you should try not to make it a habit. If you're having a hard time getting through an assignment, take notes on why. It's perfectly reasonable to bring these points up to your professor or bring them up during discussion.