What does "really" modify?
Let's say that Tom knows a few thousand Chinese characters and -- with the aid of a dictionary -- can read a newspaper article, But he cannot speak or understand Chinese when spoken to him.
Thus, we would say, "Tom does not really understand Chinese,"
Some experts say that "really" modifies the verb "understand"; some experts say that "really" modifies the whole sentence (since it means "in fact").
May I have your opinion?