"What you say?"

One of my coworkers said today "what you say?" to me because he could not understand me but im wondering whether he was mocking me or is it a correct way asking for repetition?

and by the way i distinctly heard What not What'd

Some people say that. Native speakers say it. He could have been mocking you or he could have been sloppy in his speech. It isn't really correct. Perhaps he is less educated than you are. Let it roll off your back and don't worry about it.

Was it "What you say" or rather "Whachu say?"
The second is fairly common among American English speakers of a certain age/education level.
Mostly, in asking for someone to repeat, we just say "What?" or even "Huh?"