It's more "fully comprehend all aspects". You could also say "get" or "understand" or "know" as synonyms for comprehend (in the right context).

Grok works in English, I've been reading it for, what, 20 years in English texts. It mightn't be in dictionaries but they're not the sole arbiters of language.

It comes from US English, AFAIK, a neonym from Heinlein (the sci-fi writer).

I believe it's in both Oxford and Merriam-Webster.

I use "grok" in my writing. Sometimes an older person (usually a boomer or Greatest Generation reader) doesn't get it. Usually the Gen X and younger people understand what it means. Anecdotal, FWIW...

I always just figured it was programmer speak and used it accordingly.

English speakers seem to have this weird idea that all people need to use language that everyone can understand.

Other languages tailor their speaking patterns given the class, context, and people around them.