In D&D 5e, I can't find a skill check for identifying monsters. (Other than Arcana for planar monsters). Can PCs identify monsters, and if so, what skill should they use? (Or is it just a Wis/Int check?)
It's almost certainly going to be Wis and Int Checks. The question is which skill proficiencies will apply to those checks depending on what their origin is.
This is generally the Purview of the Monster Manual and DMG, however, Mearls has said that more of Basic D&D is will be released this coming week. We should know a lot more when Basic D&D expands.