Definitely coordinate with the parents, not only to find what your nephew's interests are but also so no gifts are duplicated.
If they don't have advice or you can't ask for some reason, Brio scale trains, construction equipment, emergency vehicles, dinosaurs and generic toys are usually a good bet, they don't usually understand or care about brand names or franchises yet.
if they don't have some already, 100% on the Brio train set - except not Brio. The generic wooden railway sets are just as good nowadays, and many many times cheaper.
You can buy a whole dinosaur themed wooden railway set on Amazon for £37. I'd want that, even as an adult!
FWIW, both of my kids played with their wooden railway for years - seriously good investment.