Always have a question on questions open
To better communicate with the students construct a simple question and make it anonymous. Here is an example,
What questions do you have?
Then have this question always available for students to give their input. This is in addition to the question or questions you have activated on the student web page dealing with your current content.
You can quickly view responses to this question by toggling between the "eye" icons for multiple questions on the admin page.
Answers to this "question on questions" often generates the best insight on student understanding since the open-format questions for your content usually constrain what is being asked.