Does Notepad++ show all hidden characters?

In newer versions of Notepad++ (currently 5.9), this option is under:

View->Show Symbol->Show All Characters

or

View->Show Symbol->Show White Space and Tab

Yes, it does. The way to enable this depends on your version of Notepad++. On newer versions you can use:

Menu View → Show Symbol → *Show All Characters`

or

Menu View → Show Symbol → Show White Space and TAB

(Thanks to bers' comment and bkaid's answers below for these updated locations.)

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On older versions you can look for:

Menu View → Show all characters

or

Menu View → Show White Space and TAB