Carlitos Wayne was a made man working as a minor member of the Omertas at the Gomorrah hotel and casino. Unfortunately for him he ran afoul of Omertas lieutenant Cachino over his relationship with one of the prostitutes, Joana. Since Cachino also wanted her, he accused Carlitos of stealing Omertas funds and put a price on his head. Since then, Carlitos has been on the run.
Carlitos is hiding out in Vault 21 hotel as a guest of Sarah Weintraub. He can be typically found in the hotel's diner sitting at a back table.
Alternatively, Carlitos may be located in a back room away from the hotel's patrons as befitting a man on the lam. Your objective marker should lead you to him.