x2Watch and LearnIf your opponent's Pokémon used an attack during his or her last turn, use it as this attack.
Can I use Sudowoodo's "Watch and Learn" attack to copy an opponent's GX Attack used on their previous turn? If yes, does this count as my GX Attack for the game? And if I have already used my GX Attack for the game, does the "Watch and Learn" attack fail?
Yes, yes, and sort of. If you have already used your GX Attack you can still use Watch and Learn, but the effect of the copied GX Attack would fail.
What happens if my opponent failed a Confusion check last turn and I try to use Sudowoodo's "Watch and Learn" attack? Would Sudowoodo take 3 damage counters?
If the Pokemon failed its attack because of Confused, an attack was not used. Sudowoodo's Watch and Learn would simply do nothing.
If my opponent used Zoroark's "Foul Play" attack their previous turn, could I play Guzma to bring up a benched Pokemon and have Sudowoodo's "Watch and Learn" attack use "Foul Play" to copy one of the new Defending Pokemon's attcks?
Yep, that works.
If I use Sudowoodo's "Watch and Learn" attack on the turn after my opponent's Mew EX used its "Versatile" Ability, can "Watch and Learn" copy the attack that Mew EX used?
Yes, that works.
If my opponent uses Sudowoodo's "Watch and Learn" attack to copy the attack my Pokemon used last turn, what would happen if I use my own Sudowoodo's "Watch and Learn" attack on my following turn?
Your Sudowoodo would copy your opponent's Watch and Learn attack, not the attack your opponent copied. So unfortunately your Watch and Learn would do nothing.
Say my opponent's Rattata used its "Dangerous Suspicion" attack which moves it to the Bench. On my next turn, could I use Sudowoodo's "Watch and Learn" attack to copy "Dangerous Suspicion"?
Yes, you can. A Pokemon being benched or leaving play does not keep the attack from being copied by Watch and Learn.