Both comprehension and understanding can be used to talk about someone's ability to understand something. Comprehension usually used with of. Or about how something works:
Qatar Airways switches to Avios your miles with British
The meaning of understanding is a mental grasp : Understanding is a relation between the knower and an object of understanding. Understanding implies abilities and dispositions with respect to an object.
He noted bond's apparent lack of.
Mental process of a person who comprehends; How to use understanding in a sentence. Knowledge about a subject, situation, etc.
