I suspect that a "Papuan" clown is simply a clown sourced from New Guinea. My understanding of an "onyx" clown is that it is a percula clown which is black. A Papuan clown may or may not be "onyx," depending on its coloration, and an "onyx" clown may or may not be Papuan, depending on its source. (Not to be confused with something like "Rod's Onyx clowns," which, I understand, come from a particular captive-bred strain of clowns.)