The critical notion of metacognition is either you know what you know, or you know what you do not know.
How could we know that? Express to others may be one of the answers to it.
If we express others our knowledge, we could get the idea of where we are stuck in.
Therefore using some ways(three options followed) to get ideas out of the brain is very helpful.
Writing/Blogging
Explaining the information to others.
Talking to yourself about the knowledge you learned.