For the Leave No Man Behind quest in Gray Zone Warfare, you are tasked with tracking down the person who was murdered near the town hall. Not only do you have to track down the body, but you also have to place a GPS tracker on it.
Leave No Man Behind Task Guide for Gray Zone Warfare
You can expect the town hall to be heavily guarded when you get there. Also, the exact location of the body will not be known. You will need to track down that part of GZW and use nearby clues to determine your exact route. And just like Gunny's previous mission, you also need to remember to pack a crucial item.
The exact location of the body is near the Town Hall, but the location of the Town Hall differs per faction in Gray Zone Warfare.
Before you leave Base Camp, make sure you have at least one tracker in your inventory. Gunny will give you one if you accept this quest in GZW, but if you die trying, you will likely drop it. Gunny sells them for $50 at the bottom of his vendor.