Not sure what you meant, but you can permanently turn showing whitespaces on and off in Settings -> Editor -> General -> Appearance -> Show whitespaces.
Also, you can set it for a current file only in View -> Active Editor -> Show WhiteSpaces.
Edit:
Had some free time since it looks like a popular issue, I had written a plugin to inspect the code for such abnormalities. It is called Zero Width Characters locator and you’re welcome to give it a try.