grammar - Using が multiple times in one sentence

If you ask a question, such as 誰がこれが分かる？ Is this still grammatical? Is it okay to use two が's in the same sentence?

Answer

Yes, it is grammatically correct. But if you want to avoid multiple がs like this, you can replace the former with に.

• 誰にこれがわかる？

See also this topic about が and に interchangeablitily.