#show
This will display the correct icon, assuming you use the red question mark.
You can force it to display any spell/ability which your class/race gets, or any item your toon possesses.
It does not give you a mouse-over tooltip.
You can #show Elemental Mastery, and /cast Lava Burst, for example.

#showtooltip
This is as the above, except you can mouse over the icon for the tooltip.