When I have a Splash Energy attached to for example a Greninja and it is knocked out, may I also return the Froakie and the Frogadier to the hand or is it just the Greninja I may take back on my hand?
Just like with AZ and Rescue Scarf, returning a Pokemon with Splash Energy attached to your hands means putting all the Pokemkn cards," -- the Basic and all Evolutions into your hand. If your Greninjs BREAK with Splash Energy is Knocked Out, all of the stages go back to your hand. You only discard non-Pokemon cards such as Tools, Energy (including Splash Energy itself), etc.