Some consider this "Pittsburghese". Many people in Pittsburgh speak so quickly and with so little enunciation, that you often get phrases like "J'eat yet" or something about the Steelers and drinking into a three word sentance.
This particular phrase, however, is merely, "Did you eat yet?" Although, it can also sound like "Jeat jet?".
"Hey Bobby, I was going out for food, j'eat yet?"
"Not yet Jane, I'll come grab food too."
"No, I got a sandwich now though."