To me it looks like it definitely hit him side of the head almost directly in the temple area. The way he's woozy and then puts his hand on his eyebrow/forehead to me signifies an instant pressure he's feeling behind his eye (I'm thinking about times I've been hurting that make me put my hand in a similar area). He probably felt tons of throbbing.
Not sure what to make of it, but Hags did say he was in the hospital and that him and Brassard said they wanted to win it for him. So there's definitely concern there. Thankfully he has time to heal but this most definitely could also be something very serious. Even if not, I think he misses a game or two at the minimum. If you've ever been hit in the head like that you know it takes at minimum, with no other complications, at minimum, a week or week and a half to be symptom free. And holy hell McDonagh, what is it with you and causing freaky injuries to our guys??
And on edit: No, it's not his jaw. And he's probably in the hospital being evaluated for internal bleeding or swelling. Being hit there that hard is no joke, and can cause very dangerous complications. Wouldn't surprise me at all if they hold him there a few days to fully evaluate.