The phrase "knew what what" refers to a situation in which someone is aware of some secret or hidden knowledge. When referring to this concept, there are several synonyms you can use to describe the person's understanding. Some options to consider include "understood the implications," "was privy to," "had insight into," "was in on the secret," "knew the score," "had a handle on," or "was familiar with the details." Each of these phrases conveys the idea that someone has knowledge about something in a way that others may not. Using these synonyms can help you add variety and nuance to your writing, making your descriptions and characters feel more dynamic and complex.