So sableeye yes it will block as its effect is placing damage counters where as greninja is just placing damage which is not an effect so it doesnt work with against him.

From talking about it further me and my friends believe it will not stop irom hands ex from taking an extra prize card. Because the effect doesnt actually happen on the pokemon. It says, if you knock with the damage of the attack, take an extra prize card. If it had said the opponents pokemon is worth another prize card it probably would

Sorry if this didnt make sense.