I could see the rationale, but "Who is the giver of this bag", is a very odd English indeed. "Who is the bag giver" is equally odd. So, why couldn't it simply be translated as "Who gives this bag?" However there is an occupation called "care giver".
I put "Siapa yang pemberi..." I still don't understand why this is incorrect. How can we know when to use "yang" in a "Siapa..." question?