If your goal is to use the relative clause “whose job is to help students acquire knowledge” then the clause is correct but you don’t have a verb in your main clause. For example if you eliminate your relative clause, the rest “A teacher” isn’t a sentence. One of the ways to fix that is the one Gary gave. Another is to continue your sentence. For example: “A teacher whose job is to help students acquire knowledge should always work to improve their skills.” Then when you remove the relative clause you still have a valid sentence.

I don't know about relative clauses, but isn't that every teacher's job? Or did you mean "A teacher is someone whose..."