I think PHGamer answered that already: an accessory. Presumably some kind of dongle.
But there aren't any ports on it.
The hypothetical dongle would get electricity via the iPad port and then would expose a surface that would leverage the magnetic coupling/inductive charging for the Apple Pencil in the same way that it works now. Might not be the most attractive dongle but I don't think there's anything physically impossible in engineering something with the capabilities needed to allow charging...