Subject clause means that a clause acts as the subject component of the main clause, for example, it is certain that he will come to the party. The main clause is that that's for sure. That is the formal subject of That is certain, so it is called the subject clause.

I wonder where you still work in the factory.

You are still working in a factory, which is what I want to know, so it is called an object clause.

This is the room where he lived five years ago. The main clause is that this is the room. He lived in this room five years ago. Clauses used to decorate rooms are called attributive clauses.