API C PetJournal.GetSummonedPetGUID

Returns information about a battle pet. summonedPetGUID = C_PetJournal.GetSummonedPetGUID

Returns

 * summonedPetGUID : String - GUID identifying the currently-summoned battle pet, or nil if no battle pet is summoned.

Details
Blizzard has moved all petIDs over to the "petGUID" system, but left all of their functions using the petID terminology (not the petGUID terminology) except for this one. For consistency, the term "petID" should continue to be used.