Students can ask questions anonymously before, during or after a lecture by going to a Lecture page and tapping the ✋button.
If a question is asked anonymously, it does not go "live" immediately, i.e., nobody except professors can view the anonymous query.
This is unlike a query asked without the use of the anonymity option, which becomes visible to the entire class as soon as it is posted.
Anonymous queries would show up on your page as "Pending Approval".
Here, you can tap on this query and "approve" it. Once you approve the query, it will go live and be visible to everyone in your course.