If a Pokemon is sleeping and you use Sucker Punch, will the move fail? What if the opponent tries to use an attack? What about Sleep Talk? What about Snore?
Yes as long as the Pokemon is attacking whilst asleep sucker punch works. Same things for snore. Sleep talk is a status move so sucker punch fails.
If the opponent uses Sleep Talk or Snore, then it still counts as an attack, and the Sucker Punch will hit. But if the opponent is just asleep, and does not manage to use a move through the two moves above, then the Sucker Punch attack will fail.
