Didn't even know about until I finished watching the movie and was reading some light trivia on it. Anyways, what's the joke you are asking. Here you go:

"the character played by Asian-American Jin Au-Yeun asks his counterpart "what kinda knees are these," referring to himself. There's no response and a few seconds later he says "Chi-knees.""

Apparently that was enough to get the movie banned in China and chinese people up in arms and lead to review bombing etc.

As far as the movie goes, well, it's pretty stupid but it's entertaining and an easy watch. Basically Monster Hunter gets the Resident Evil movie treatment where they shove Milla Jovovich in the movie as some character that has absolutely nothing to do with the game franchise.