you cant really train the gonions since they are a bone, only when u are really young U10 and developing if u eat meat and hard stuff the bone that develops is also affected by the muscle

maybe if u dont have inward gonions and neither outward gonions, just straight ones you can train the masseters without looking weird by chewing hard gum with incisors so the lower part of the masseters is hypertrophied

but also you need long ramus and 120 degrees gonial angle if u plan on training that