Encodings in Emacs.

[Nacho]

Hello.

I have been using Emacs to write and edit japanese files and I would
like to ask you something I have not found how to do.

When I write text, I know how to change the encoding of the buffer to
save it with the encoding I want, for example, EUC-JP, ShiftJIS, etc.

When I open it again, I have not to tell Emacs the encofing of the
file, he knows the encoding used.

How can I know in what encoding is the file?

Also, if I want to read a file in a specific encoding, how can I do
that? Or similarly, to change the encoding of a buffer but re-decofing
it. That is, if I  change the encoding with M-x
set-buffer-file-coding-system it doesnt reencode the buffer. The use I
want to do to this is when I read a file with several codings mixed
(ShiftJIS and EUC-JP) and I want to read both.

Thanks a lot in advance.

Best regards.