Emacs, describe-key Command, C-h k
emacs
Solution
`C-u` is provides a prefix argument to the function called after it (as you can see from its docs). Access the documentation for `M-.` and then look there for what happens when the function receives a prefix argument. There's no separate documentation for `C-u M-.` since it is not separate function.
Problem
When I want to find the command bound to C-u M-. using C-h k, it turns out that emacs gives me the command bound with C-u. What should I do ?