What should we do? 어떡해야 돼?
What should I paint? 뭘 그려야 되지? (asking for suggestions because you are out of ideas)
What should I paint? 뭘 그려야 돼요? (asking the teacher what she/he already decided on what you should paint).
What should I write? 뭐라고 써야 돼?
You should think well before you buy something. 뭐 사기 전에 잘 생각해야 돼.
It should have been me who died, not you. 죽었어야 하는 사람은 나인데, 너가 아니고.
Should that person over there really be at this party? 저기 있는 저 사람 이 파티에 있어야 돼?
This math test shouldn't be this hard! 수학 시험이 이렇게 어려우면 안 돼! (or 수학 시험이 이렇게 어려워야 돼? This one is kind of a rhetorical question)
Life shouldn't be easy. 사는 게 쉬우면 안 돼.
As you see, -야 되다 applies to most cases, except for "should have + past particle" and negative sentences.