When is "egy" omitted? I thought it could be dropped on a sentence which expresses where something is "where can I find a car" can be translated into something without an "egy" right?
Yes, that is correct. I guess you could omit it here, as well.
Well, it kills a possible interpretation of the sentence - talking about one certain (but possibly unknown) man. It would sound more like "Where do you see (some) men?" Even the amount is unsure.