How to show all characters in a specific line

[Harry Putnam]

How to show all characters such as \t and any others, printable or
not.

What I'm after specifically is to find a piece of code I once snagged
probably here... long ago.

It worked like the :l (:el) command in vim

In vi/vim on any line and in Command mode if you press :l <RET> you will
see any \t, newline and etc.

Great for conf files that require tabs between elements or anywhere
you don't want space before the newline.

Someone helped me write that or at least edit existing code to suite.

Can anyone point me in the right direction... perhaps there are
existing emacs commands that do the same thing?