How to see the file’s encoding in emacs?

Question

You have several ways to get (and set) the buffer encoding:

You can see with the U in the mode-line that your buffer is in “Unicode”, if you put the mouse over it, it will show in a tooltip the current buffer encoding.
you can also see the current encoding with C-hv buffer-file-coding-system RET
you can change the whole buffer encoding for next save with C-xRETf
you can also change the detected encoding to force an other one and reload the file with C-xRETr
you can set an encoding for the next I/O command only with C-xRETc
there are some other possibilities, take a look on C-xRETC-h

Fix and diagnose:

Inside a buffer, if you are interested by a single character encoding / details, put the point on a chinese char and C-uC-x= will help. (The same without the C-u shows only a few informations about the character, and the encoding is not part of it.)
examine the file by yourself:
- you can open a text file without any decoding or heuristic with M-x find-file-literallyRET
- or you can go closer to the metal (hex editor) with M-xhexl-find-fileRET or for current file M-xhexl-modeRET
if the file is a mess with mixed encodings, you can fix portions with M-xrecode-regionRET