On the left side of the modeline, you'll see
(DOS). This means that Emacs is viewing the buffer as if it had DOS-style line endings. To view the buffer as if it had Unix-style line endings, use the command
revert-buffer-with-coding-system (bound to
C-x RET r or
C-x C-m r), and select something like
utf-8-unix. Then the
^M characters will be visible.
Alternatively, if you want to convert the file to Unix-style line endings, use
C-x RET f/
C-x C-m f) and choose
utf-8-unix, then save the buffer.
From the Emacs manual, 22.6 Recognizing Coding Systems:
Emacs recognizes which kind of end-of-line conversion to use based on the contents of the file: if it sees only carriage-returns, or only carriage-return linefeed sequences, then it chooses the end-of-line conversion accordingly. You can inhibit the automatic use of end-of-line conversion by setting the variable inhibit-eol-conversion to non-nil. If you do that, DOS-style files will be displayed with the ‘^M’ characters visible in the buffer; some people prefer this to the more subtle ‘(DOS)’ end-of-line type indication near the left edge of the mode line (see eol-mnemonic).