To "take it on the chin" is an idiom meaning to accept defeat, insult, or penalty. "Cop" can be slang for "take" or "receive" in certain situations. So this looks like an idiom that's been altered with slang. Of course it could also have the literal meaning, to receive a punch or hit on the chin. Hard to tell without the context.

"cop something on the chin" = to take responsibility for your actions

Could you provide more information about the context?