Knowledge is information; understanding is what we do with it.
Knowledge relies on the system/instruction/artifact already existing. It tells us how to do the thing or what the thing already is. It shows what is already there.
Understanding doesn't just acknowledge the existence of the knowledge artifact, but sees how it works and how that process might apply to something that does not yet exist.
Knowledge is retrieval whereas understanding engages with the possibility of creating something new.
Knowledge is passive, understanding is active.