Most questions occur to me outside of class, when I'm reading a textbook or working on an assignment, so I e-mail my math professors with questions. Otherwise the alternative is wait until next class which can be anywhere from Tuesday to Thursday, Thursday to Tuesday, or once per week. I have had a few professors complain, though, that $6$ or so questions is too many for a F2F course.
From your experiences, is it typical to have, $6$ or so questions in a week of the course readings and assignments? Do you ask your professor all these questions, or ask some of them here on math.stackexchange?
(If this belongs on meta.math.stackexchange, please let me know and I'll move this question there.)