Hi! I’m Asian and was raised in North America. I would say that your character should have the culture of the place they’re in/ grew up in, but maybe still celebrate Korean holidays? It definitely depends on how many generations of his family were raised in North America. They probably have good English, but speak Korean at home. HOWEVER, don’t take my word for it. I am 98% Chinese and only 2% Korean, and Asian countries vary hugely. I’m just stating from my personal experience, which will likely differ from a Korean person’s
Do you have Instagram? You should check out pinkmantaray. He’s a trans half Korean in NA with a vocal platform about what its like to be trans and Asian and just LGBTQ rights in general.