Rohtu is waiting for you as soon as you enter Lahtenda Bog. Click on him to get him to join you, then follow the quest marker to the main Corsair camp. They are just past the corpse of Rohtu's mother, where you found it in Wandered Off Again. There will be five random Corsairs, between levels 10 - 12 (in addition to the random wandering Insects and Mandragors you will encounter along the way). After the corsairs are dead, Rohtu will run back to his mother's corpse to grieve and you can collect your reward.