Generally, I know I learned after reading because I am able to answer questions concerning the reading. Also,  not only able to answer a question regarding the reading, but I am also able to explain why I gave a particular answer. To ensure that I learned the most important concepts in the reading, I make sure that I write it boldly in my notes for the purpose of studying. Thus, I would be able to recognize what information is most important. Also, to ensure I learned the most important concepts in the reading I make sure that I am able to elaborate on main topics as well as  subtopics.