Jajangmyeon is a carb bowl. 300g of cooked noodles is 420 calories on its own, and the sauce adds another 130g of stuff that is mostly onion and potato cooked in black bean paste. The pork dice is small, maybe 40g. So you get 27g of protein and 129g of carbs, roughly the ratio of a plate of plain pasta with a spoon of sauce.
The oil is where restaurants differ. Chunjang is fried in oil before the vegetables go in, and a generous kitchen uses 2 tablespoons per portion, which is 240 calories of oil in the sauce. The MFDS survey found bowls ranging from 400g to 840g across shops, so a big-portion place can be serving you 1,000 calories in one bowl for 7,000 won.
Ganjajang (the dry, freshly stir-fried version) is listed at 825 in the same survey, slightly higher because the sauce is cooked with more oil to order. Jjajangbap swaps the noodles for rice and lands around the same. The set that really adds up is the half-and-half with tangsuyuk on the side, which turns lunch into a 1,300 calorie sitting.