Interestingly DuckDuckGo gives you a box with the Emacs command when you search for "C-x n" (although the quick reference they link to doesn't even include that command). Of course, if you want to know what a shortcut does in Emacs, you can just use "C-h C-h c <the shortcut>". Or if you want to know what a function does and what it's bound to, "C-h C-h f <funtion>".