To have an edge means to have slight advantage or superiority over someone else.

Let's say you & your sister like sweets. Your mom has kept sweets at the shelf located 7 ft above ground. Your height is 6' 2 & your sister's height is 6'. Since you are taller, your hand can reach the sweets easily & thus, you have a edge over her while getting sweets.

Now, coming back to your question; this is what the conversation means.

The first man said, "You can ensure that my superiority remains intact".

The second man said, "You need to have a superiority in first place to actually make it remain intact"... (Means the second man feels that the first man doesn't have any advantage/superiority in fact....that is he doesn't have any edge)