Class Quest at Military Academy (Counter-Attack Skill)
 

How exactly does this work? I swear the game is messing with me because at times I had a 1 or 2 of 20 skilled warriors killed listed but now I'm finally done with everything on Debir, I checked and it's back to 0.

Is that a bug or what exactly does count as a skilled warrior? I'm playing Gold (German) version, if that helps any.

Nowhere in quest info is said you need to kill 20 warrior units (knight, horseman, assassin) on Debir island. Go to Scarlet wind, Rusty anchor . . . when you get enough killed units (and finish some other quest, gather gold, more lds . . . ) go back to Debir and take reward and open skill in hero window.
As for counter itself it must be bug, or it`s just some error try to find some battle that have more then 20 those units and counter should go from 0/20 to 20/20 (in gray color, like finished quest) and there shouldnt be any problems.
Good luck :-)

Never mind. It seemed the count would sometimes show up as 0 and when I clicked on another quest and then back the correct count is shown again. Currently at 14 now.