What do we call a question the answer to which seems obvious to many of us?
Rhetorical question - A question asked in order to create a dramatic effect or to make a point rather than to get an answer.
If the answer isn't obvious then the question isn't rhetorical.
An obvious question is the most common phrase - really! The phrase could also refer to a question which rather obviously poses itself in the course of the discussion in question as well.
You could also call it a trivial question, although that implies a lack of importance.