I just had the following situation with Vesuvan Doppelganger and Clone:

The enemy cast Vesuvan Doppelganger, which has the same wording as Clone "You may have ti come into play as a copy of target creature", and when it is on the stack you can see the target.

This allowed me to use bounce on the target which made the shapeshifter die when it came into play.

But then next turn the opponent played Clone, and clone had not target while on the stack, and the enemy had 2 creatures and I couldn't tell which one to bounce. Body Double also had no target while on the stack. Are these things supposed to have a target while on the stack or not? Which one is wrong?

I've also noticed some other similar situations with other cards where you can respond to the card being played but not the activated ability, but haven't made note of it. I can if it would help round them up, though. I'm not sure what the current rules on triggered abilites are, though, do they go on the stack or not?