Namjoon:
He'd make a great maths teacher.
He'd enjoy teaching his students the ups and downs and equations, and will happily help them whenever they need it.
He works hard and wishes for his students to do the same.
Seokjin:
I get nurse/ librarian vibes from him tbh, but he'd also be a really good Geography teacher. He would enjoy teaching students about how the world works.
He's not really the guy to shout at his students, but he can be pretty scary when students don't pay enough attention to him. Luckily they love him and they never provoke him.
Seokjin likes to make his lessons as fun as possible by throwing in jokes every now and then.
Yoongi:
Obviously Yoongi would make an awesome music teacher. He may seem like a quiet person but he teaches really really well.
Yoongi talks a lot to his students about his music is important and shares some old funny stories with them.
Also, he puts effort into every lesson and makes sure they learn loads even if it's a short lesson.
Hoseok:
(That gif he looks like an angel)
History would be his subject (in my opinion) and Hobi would be the type of guy who would allow his students to talk but as long as they're sensible.
He's never angry and doesn't do 'worksheets' or 'lectures'. He somehow finds a way of making his lesson fun, and sometimes he does weird funny things to make his students laugh.
At the same time, hobi hates it when they don't pay attention. He never shouts at them but can be pretty scary when angry.