Well I am not completely sure about your keyboard as you mention fn and that sounds like a laptop keyboard not a PC

However, I have a keyboard where one of the keys has 3 characters on it.

Pressing the key once gives me `
Holding the shift key down and pressing the same key gives me ¬
Holding the Ctrl & Alt key down together and pressing the same key gives me ¦

I used Notepad to test it and it worked and also on this post.

So try using combination of keys.

Good luck