Can a base runner knock the ball out of a fielders glove?

Yes, if it is a force out, as long as the fielder has the ball in his possession (glove or free hand) if he touches the bag before the runner with any part of his body then the runner would be called out.

Now if this was a play that required a tag, and the ball was in his bare hand and the tag is made with the glove, or visa-versa, then the runner is safe