If Dusknoir with the "Spectral Breach" Ability is already in play and then Fusion Strike Energy is attached to a Pokemon (either mine or my opponent's), does Fusion Strike Energy prevent "Spectral Breach" from affecting it, or does "Spectral Breach" disable Fusion Strike Energy's effects?
When Fusion Strike Energy gets attached to a Pokemon it prevents the effect of Spectral Breach, therefore providing every type of Energy and preventing all effects of your opponent's Abilities done to that Pokemon.
Source: TPCi Rules Team (2021-12-23)
If Dusknoir with the "Spectral Breach" Ability gets Knocked Out while Recycle Energy is attached to it, does the Recycle Energy go back to my hand or not?
No, Spectral Breach is still in effect when the cards are going to the discard pile, so the Recycle Energy would be discarded.
Source: TPCi Rules Team (2020-11-12)
If Dusknoir’s “Spectral Breach” Ability is active, does Double Colorless Energy provide one energy or two?
It would only provide one {C} Energy.
Source: Vivid Voltage FAQ (2020-10-31), TPCi Rules Team (2020-11-12)