Translation:Grandfather asks about grandmother's opinion.
In my humble opinion, your answer is incorrect. The original sentence suggests that grandfather has already heard grandmother's opinion, but he couldn't understand it. Therefore, "what does grandmother mean by saying that?" is the connotation. "Pertanyaan" (the same root word of "bertanya") means "a question". "Bertanya" + "tentang" should be "ask about" (the topic).
If you say "ask for", that means grandfather is requesting an opinion from grandmother (i.e. he hasn't heard her opinion yet). In this case, you use "meminta" instead.