[common; from the novel “Stranger in a Strange Land”, by Robert A. Heinlein, where it is a Martian word meaning literally “to drink” and metaphorically “to be one with”]

The emphatic form is “grok in fullness”.

1. To understand.

Connotes intimate and exhaustive knowledge. When you claim to “grok” some knowledge or technique, you are asserting that you have not merely learned it in a detached instrumental way but that it has become part of you, part of your identity.

— The Jargon File