Should be possible to find all registered global shortcuts from the keyboard shortcuts dialog
I recently notices that Alt+leftarrow was not working anymore, which made life in intellij a little hard since that was mapped to back (and that is something my fingers do automatically). After some investigation I realized it was something in my setup that was stealing this shortcut, but it was not listed in the control center keyboard shortcuts dialog. So I had to spend quite some time to try to figure out what was causing this, in ways normal (non-tech geeks) users may not be able to.
If an application (or gnome-shell extension) asks mutter to steal a global shortcut for it, I would expect it to be listed in the control center keyboard shortcuts.