Use /map to find the waypoint for the Hibernian Commander. Waypoints are red dots on your map which indicate the location of quest objectives, such as enemies to be killed or NPCs to interact with. Afterwards, return to the Commander Kneeland.
I think you're ready for a bigger challenge than these pathetic foot soldiers. We need to start looking for the leaders of this siege. They must be closer to the water, the cowards. Go down there and kill one of their Commanders!
Good work, *name*! It certainly served him right!