I have a ASUS ux330ua and the problem is that the fn shortcut for the volume works but the other shortcuts don't. Can somebody help me with this?
Screen Brightness Keys
I have the same problem on a UX305FA, and here's what I did to address it. Rather than pulling my hair out over the issue,
I installed xbacklight, a command line program for changing screen brightness
sudo apt install xbacklight
Then I set custom keyboard shortcuts that run xbacklight to increase/decrease the brightness. I couldn't get Fn+F5/F6 to work as a binding, so I use +F5/F6 instead.
I don't remember the exact commands I used with xbacklight, but the man page should have enough to get you going.
As for the other keys, I didn't attempt to get any of them working, but you might be able to work out something similar with those as well.