Say I have Keldeo GX already in play, and my opponent uses Latios GX's "Clear Vision GX" attack with Power Plant in play. If I play a different Stadium to get rid of Power Plant, can I use Keldeo-GX's "Resolute Blade GX" attack now?
Yes, you can. When Power Plant is removed Keldeo GX's Pure Heart Ability turns back on, and Keldeo GX is no longer hit by the global effect of Clear Vision GX. If an attack does not place an effect on Keldeo GX directly, like an attack that puts an effect that isn't removed when returning to the Bench, it can be removed by reactivating Pure Heart.
Source: TPCi Rules Team (2020-02-06)
What happens if I put a Keldeo GX with "Pure Heart" Ability into play after my opponent has used Latios GX's "Clear Vision GX" attack? Would my Keldeo GX be able to use its "Resolute Blade GX" attack or not?
As long as the Pure Heart ability is not blocked or turned off when Keldeo GX comes into play, it would be unaffected by Clear Vision GX.
Source: TPCi Rules Team (2019-12-05)
If my opponent has used Latios GX's "Clear Vision GX" attack, would my Keldeo GX be able to use its "Resolute Blade GX" attack?
Yes. The effect of Clear Vision GX is placed on each of the opponent's Pokemon, and since Keldeo GX's Pure Heart Ability prevents all effects of attacks done to it by your opponent's Pokemon GX, it is unaffected by Clear Vision GX.
Source: TPCi Rules Team (2019-09-05)
If my opponent used Latios GX's "Clear Vision GX" attack on me, could I use Channeler to remove that effect?
Yes you could, because Channeler removes effects from both you and your Pokemon.
Source: TPCi Rules Team (2019-08-01), TPCi Rules Team (2019-09-05)
If my opponent used Latios GX's "Clear Vision GX" attack on me, could I use Bonnie to allow my Zygarde-GX to use its GX attack?
No, you cannot. Although Bonnie would normally let Zygarde-GX re-use its GX attack, the effect of Clear Vision GX is on Zygarde-GX and that still prevents using *ANY* GX attacks.
Source: TPCi Rules Team (2019-09-05)
If my opponent has used Latios GX's "Clear Vision GX" attack, do I get to draw 7 cards if I use Hala?
If you already used your GX Attack before Clear Vision GX, then yes you get to draw 7 cards for Hala. Otherwise no, getting hit by Clear Vision GX doesn't mean you have used your GX attack for the game.
Source: Unified Minds FAQ (2019-07-19), TPCi Rules Team (2019-08-01), TPCi Rules Team (2019-08-29)
If my opponent has used Latios GX's "Clear Vision GX" attack, can I use a GX attack that ignores effects?
No, because you don't even get to start using the GX attack.
Source: Unified Minds FAQ (2019-07-19), TPCi Rules Team (2019-08-01)