Welcome to LQ.
You have probably looked at these links already:
I suggest that you look in:
and look under option
for compose, altwin etc and see if there is anything suitable for your requirements.
If there is, then open Terminal:
gksudo gedit /etc/default/keyboard
Then enter the desired key value between the quotation marks in:
Save the modified file and exit.
My Compose key options on a UK keyboard are:
Compose key Position of Compose key
compose:ralt Right Alt
compose:lwin Left Win
compose:lwin-altgr 3rd level of Left Win
compose:rwin Right Win
compose:rwin-altgr 3rd level of Right Win
compose:menu-altgr 3rd level of Menu
compose:lctrl Left Ctrl
compose:lctrl-altgr 3rd level of Left Ctrl
compose:rctrl Right Ctrl
compose:rctrl-altgr 3rd level of Right Ctrl
compose:caps Caps Lock
compose:caps-altgr 3rd level of Caps Lock
compose:102-altgr 3rd level of <Less/Greater>
compose:sclk Scroll Lock
Under xev, my Right Windows
key is 134
and this is the Super key
(keycode 134 keysm 0xffec, Super_R), NOT the Compose key .
Your one may in fact be the Compose key as you stated in your post.
Please double-check this.
If your Right Windows key is the Super key then you are okay.
If your Right Windows key is the Compose
key, then change it to the Right Alt
(AltGr) key by entering compose:ralt in XKBOPTIONS=""
This will free up the Right Windows key to be used as the Super key.
By the way, all the Finnish keyboards I found looked nothing like your one.