How to show XYZ coordinates without the 'Fn' key?
Just press F3.
If your keyboard does not have Fn, then odds are, F3 works as normal. No keyboard manufacturer would require Fn+F3 without providing a Fn key. That doesn't make any sense.
You seem to be on a Mac. On there, you should open System Preferences, go in Keyboard and enable the use of Function keys as delfault actions. I had to do this too on my Mac!