The waffle batter is flour, sugar, egg and margarine, cooked on an oiled iron, and a folded kopitiam waffle weighs about 100g. That is 300 calories before anything is spread on it. Kaya is coconut milk, egg and sugar, about 280 calories per 100g, and the stall uses about 30g, so 85. The total of 400 is the same as a bowl of pork porridge plus a you tiao, for something you eat in four minutes.
The spread menu is where it climbs. Peanut butter is about 90 calories per tablespoon and a peanut butter and kaya waffle is about 500. Chocolate spread is similar. Butter and kaya, which is the kaya toast combination in waffle form, is about 460. The plain waffle with nothing is 300, and honestly the waffle is sweet enough on its own that plain is not a punishment.
The size varies a lot between stalls. The old style confectioneries make a thin, crisp waffle that is closer to 80g and about 330 with kaya. The newer stalls with the thick Belgian style irons make a 150g waffle that is about 450 before spread. If the waffle is thick enough to hold a scoop of ice cream, it is a dessert plate, not a snack.