Neither.
You play Unown Q to your bench.
If you choose to use it's Power, at that time, you would attach it to one of your Pokemon. You can't go straight from your hand to attaching it to a Pokemon. Note that some people use a shortcut and do that. But that's a shortcut. They are really putting it on the bench first, even if they're "skipping" that part.
IF it had anything attached to it when you used its power, those cards would be discarded. However, there is no requirement that anything has to be attached. That language is just there to tell you what to do if there are cards attached.