I really hated studying things at school I didn't need to. Sometimes the lessons were not about the topics we were studying. Or the topics had no relevance to the real world. I really hated studying things at school that I would never need in life. I rarely use Pythagoras' theorem these days. I have tried to provide examples of the correct word order.

Either is fine.

They're both ok. My own preference would be the 2nd sentence.