There is nobody John works with who doesn’t love him.
(The sentence means to say that everyone with whom John works loves him.)
What is the core problem in this sentence? The obvious problems that I'm seeing are a too-far antecedent for "who" and a misplaced "John works with" modifier.
Is there something else I'm not seeing? Could the problem be in the syntactic expletive ("There is …") construction itself? (My brain is insisting that expletives like these should be used only for expressions of states and existences, but I can't get it to think deeper.)
To resolve the misplaced modifier and far-antecedent problems, I would have rephrased the sentence as something like
Among the people John works with, there is nobody (not one) who doesn't love him.