I've been searching for a couple of days now, mainly here on Curse but also on google. Been looking for a script to check if the player is mounted, and to trigger diffrent events if player is mounted/unmounted. Even downloaded a couple of mods and read through the code but couldn't find the spot.

It should check auto, not with a button click. Any suggestions?

As a 'script' no but you can do this with some Lua if you want to write your own addon. Not sure exactly what you are trying to do but it's not so hard.