From MEPIS Documentation Wiki
If you want to find out how a particular key is mapped, open a terminal and type:
xev|grep -i keycode
then click the key that interests you. The Windows key, for instance, returns this response in MEPIS 11:
state 0x40, keycode 133 (keysym 0xffeb, Super_L), same_screen YES,
and you could then use the code "133" to remap that key.