The diagram doesn't make sense. All it showed a ground wire hooked to an NPN transistor and nothing on positive wire.
If you want to use your clock radio hook the positive wire to the terminal on the volume knob and ground wire on ground. Use a probe on the terminals on the volume pot and when you hear a buzz you found it. You have to be touching the probe to make it work.
There may be two terminals that will buzz, one will be controlled by the knob and the other is straight to the amp.