Boot into Workbench, make sure that Workbench is active (click once on the Workbench backdrop) and hit +. If your right Amiga key is working, a window should pop up, asking you to enter a (DOS) command.
If your right Amiga key does not work, select "Execute Command" from the menu, this will have the same effect.
Enter "newcli" (without the quotes of course) into that window and hit . Now you're at the console. If CTRL is working, + should have a different effect than just . IIRC, + should have the same effect as . If + just prints "m", your CTRL key is broken.
Now close the console window and move the mouse over some icon. Hit + -> this simulates a click with the left mouse button. If the icon does not change its status, your left Amiga key (or your left Alt key) is broken.
