I'll start with the definitions of both. Employment discrimination is discrimination in hiring, promotion, job assignment, termination, and compensation. Job discrimination is discrimination in which disadvantaged groups have less access to better paying jobs. Those are the dictionary definitions, and though they are slightly different I've never seen Job discrimination used. Employment discrimination pretty much covers both.

Well, I've never heard "employment discrimination" so far. But I would guess it's the same as "job discrimination". Eventhough I'm not sure.