To obtain The Art of War side quest in Dead Island 2, speak with Rosa at the Serling Hotel on Ocean Avenue. (We did this post game but you might be able to do it sooner!) For this quest, head to the Metro to look for her friend’s stash. Once there, make your way to the western side of the area where you’ll find a laptop.
Once you interact with it, waves of zombies will spawn. Clear them out until it loads then use the laptop to find out what’s loaded on it. The location of the gang’s supplies in the train cars will now be marked on your map. Make your way west towards the objective. When you arrive you’ll have to search through the cardboard boxes in the train cars to find the supplies. In the far western car you’ll find the More Than Gangbangers journal on the seat in the back of the train car. Grab it then head through the nearby metal door.
Follow the path through the tunnel and take out the crew. Grab the Javier is Disappointed journal and DBD Chest Key from where they drop. Use the key to unlock the DBD Chest in the nearby room with the workbench. Afterwards the quest will complete!