If the skinhead is not acting belligerent, yes, the Jewish guy can be required to serve him, as he has no reason beyond race to not serve him
If the guy is acting like an ass, or mistreating employees, he can be told to get the fuck out of the establishment
What if he was belligerent in the past? What if ten days ago, he was nasty and hateful to the owner but no one else saw it? Who would be in the best position to determine whether the man should be served: the owner, or a bunch of strangers who don't know either one?