It depends on what purpose I have for learning something. If it's to accomplish a specific task, then "I know enough" when I have learned enough to accomplish that task.

If I'm diving into a topic because I'm interested in it, then "I know enough" when my interest in it wanes or is eclipsed by something else.

But the majority of my generalist knowledge didn't come from either of those things, but from a lifeline habit of recreationally reading about things that are not "my usual kind of thing".