While it is obvious that familiarity is not understanding, we have nochance of knowing whether we understand something or just believewe understand something until we test ourselves in some form.
The Cornell notes practice of writing questions in the empty left column as a means of testing knowledge can be an effective tool after taking notes to ensure that one has actually learned and understood the broad concepts. They can also be used for spaced repetition purposes as well.
Valuable though they may be as teaching and learning tools, they don't figure directly into the idea of permanent notes from a zettelkasten perspective.