Noun clauses that start with "whether" or "if" are used to answer questions that you do not know the answer to. "Whether" and "if" are usually interchangeable.
Question: Is her dad a teacher?
Answer: I don't know if her dad is a teacher
Question: Are you going to the party?
Answer: I don't know whether I'm going to the party.
Question: Is he o.k.?
Answer: I don't know if he's hurt or not.