Energy » Double Turbo Energy
If I have 2 Double Turbo Energy Cards attached to one of my Pokemon, would its Attack damage be reduced by 20 or 40?
It would be reduced by 40 since each card's reduction would apply.
Source: Brilliant Stars FAQ; TPCi Rules Team (2022-02-24)
Energy » Double Turbo Energy | Abilities » Special Transfer
Can I use Dusknoir's "Special Transfer" Ability after I attack but before my turn ends to move Special Energy cards (such as Double Turbo Energy) off of my Active Pokemon?
No, once your attack ends, your turn ends.
Source: Brilliant Stars FAQ; TPCi Rules Team (2022-02-24)