So I have a thought. Cat Noir knows. In the episode Antibug tikki needs food so right now she's Marinette. When Cat Noir is hanging from the building Marinette destracks Antibug. When this happens Marinette unties Cat Noir and he said and I quote "Ladybug!?" If he could see Antibug then there is a 100% chance that he could see Marinette and therefore he knows that Marinette is ladybug. Boom therey provided.