In Islamic terminology, “knowledge” means what you know…how much Qur’an you have memorized, what Hadiths you learned, the tafsir and seerah and the positions of the madhabs you have studied, etc. But this does not denote how much you understand what you know.
Understanding is a quality of the mind, knowledge has to do with the quality and quantity of information you have deposited into your mind…you may have a great deal of knowledge, but very little understanding; and likewise, you may have very little knowledge, but you may have tremendous understanding of that which you know.