I think the word 감 you're thinking (feeling and sense, or "hang/gist" as in "I'm getting the hang/gist" of this -- this word, by the way, comes from the Chinese character 感, I think, but I could be wrong) and the word 깜 you're talking about are actually two different words.
I would say 깜 in your example loosely gets translated as "material" in English -- as in "he's not a good material/fit/candidate for that type of work", etc. And yes, as others have mentioned, 깜 is *very* colloquial...