My Wellspring Mask Ogerpon ex has a Sparkling Crystal attached and only one Double Turbo Energy on it. If I use its "Torrential Pump" attack, can I shuffle the Double Turbo Energy back into the deck and do damage to a benched Pokemon?

Yes, this is a case of doing as much as you can. You would get to do the bench damage even though you can't detach 3 energy, but you must shuffle in SOME energy in order to get the bonus. You shuffle the two energy that are attached back into the deck, and do 80 to the active and 100 to the bench (remember, damage is still reduced for the DTE since the detachment happens after damage is done).

Relevant cards

SV6_64

SV7_142

SWSH9_151