The rules say:
"Figures can only use one of their actions to attack per activation. This includes using special actions that involve performing one or more attacks (such as Nexu's "Pounce" or Darth Vader's "Brutality")."
But in the case of the wookie, his specific Skirmish deployment card allows him to special ability multiple attacks. Why would they have included a multiple attack special ability on a card specific to Skirmish if he couldn't do it? Thanks.