Actually, I can't think of any references on the show to Jerry's being Jewish. In fact, I think the only way we know he is Jewish, is that in real life, he is Jewish, and he's playing himself.
The only Jewish reference on the show at all that I can remember is the kosher meal on the plane, leading us to believe that Elaine is not Jewish.
Does anyone remember the show "Anything But Love?" In it, Richard Lewis, continually made Jewish references, many of which I thought were rather obscure . Any way, that show always seemed like a good contrast to Seinfeld in terms of the frequency of Jewish references.
Larry.