Yes, but grasp is more commonly used. It indicates a little more than knowledge, though. It means they not only have the knowledge, but can usually apply it in the right situation. Some may have a knowledge of English grammar, but not the ability to use it to speak and write.

I think so. But I'm puzzled because "hold" is not the word I would expect here. I would expect "grasp." It would be much more common to say 1 - I wonder whether he has any grasp of the subject. 2 - He has a good grasp on Chemistry.

It looks like a mistranslation - I believe I've found your misleading example on infopédia.pt The word should be "grasp". Be careful of approximate translations like this. Search for the phrase "hold of the subject" and you will see many examples of its proper use (not about knowing something, unfortunately).

It means "an understanding of" as opposed to knowledge