How does one make sure (particularly while studying for advanced level) that one has really understood what she/he had read?

Answer 1

I think I have the definitive answer for this very common question: Imagine that you are the teacher. Could you stand up in front of the class and teach a lesson on this material? If the answer is Yes, you're ready. If you believe the answer is Yes, then stand up in front of a mirror (or a willing volunteer) and try it. It may be harder than you thought, but you will pinpoint any areas of weakness.

Best wishes!