In policy matters, Trump would still be in Liberal. He isn't threatening to ban importing tropical fruit for example, and he is far more hostile to the idea of a safety net than is the Danish People's Party.
There's no way he'd be in a classical liberal party. He has, at times, said he supports universal government-provided healthcare, and he favors heavy protectionism, both of which put him at odds with liberal economics. His erratic, right-wing populist message would also not fit with a liberal party.