Don't be innocent, Zoro is wanting to find out about the King's race not because Zoro is a curious historian, but because the King's race is giving him an advantage that puts him above Zoro, so Zoro will need some something (PU) to get around this advantage.
As I said, it's like Katakuri's FS advantage over Luffy's in WCI, so Luffy needed a CoO PU in order to get around this Kata advantage.