Start with this: https://wiki.archlinux.org/index.php/extra_keyboard_keys#In_Xorg
If you’re not running X, go up a bit to the console explanation, and follow that to get your key combination number.
So there are a couple ways to get this number, You hook up a keyboard to the beaglebone, through the USB port( temporarily ), do as the link describes to “trap” the specific keycode for the key combo you want. Or do the same on an X86 Linux based system to do the same. The later here may, or may not work.