There is also this by Hoppe.
Does your father believe there is such a thing as “human rights”? If so, where did “human rights” originate? If he says something like “the UN, governments signed a UN agreement to recognize those rights” well then where did governments get that perogative? If he says something like “well, in each member-state there is an underlaying social contract on which such rights are based,” upon what does he think those rights are based? The original agreement of the people who founded the society? Well then they had to have the right to do that. (Note this is a weak argument, but it’s the foundation of social-contract theory. So you will be following the logic of his own argument in pursuing this line of questioning).
Either people have what we call “human rights” intrinsically, or they’re based on a “socially constructed contract” – the later of which begs the question because where then did they get the right to make such an agreement and have it be mutually binding.
If he doesn’t believe in any of that, then share this with him, and further ask him how he treats people and expects to be treated and on what normative grounds? Try to expose “performative contradictions” in his argument.
(I use “human rights” for shorthand. Personally I don’t think it is correct to speak of “rights” – it is correct to speak of liberty. Loose talk of “human rights” leads to such fallacies as “economic rights,” when the only appropriate thing to speak of is “economic liberty,” as a facet of liberty as a whole, for example. But getting into that would be too much detail).