There are two ways. The first is using the GOTO command, and mouse over the unit you want to attack. In the lower left of the screen, above the info box, you'll see the odd displayed.
The other way doesn't involve the goto command. Once your attacking unit is selected (waiting for a command from you), mouse over the unit you want to attack and press the ALT key. You'll see the odds displayed in a small box above the info box in the lower left of the screen.
I believe that this box could display the Xp earned in case of victory.
It' already a bit "crowded" but it would simply require the calling of an existing function, so it would simply be about the display.