For Ubuntu 12.04 LTS desktop, open the System Settings window. (If you need to locate it, search for
Settings in the
Keyboard shortcuts are under the
Shortcuts tab of the
Keyboard settings. However, I did not find a shortcut for the
Another way to go is to select Keyboard Layout and press the Options button in the lower left corner.
As suggested in a comment, one possibility is under
Caps Lock key behavior. Also look at alternate mappings under
Alt/Win key behavior or
Ctrl key position.
You may also find the answer to this question useful.
An alternative to the Super key on an old keyboard
While not (I think) providing an answer to your question, this community wiki question may provide additional information which you may also be interested in.
What are Unity's keyboard and mouse shortcuts?