To unlock the Fuel Tank trophy in Sniper Elite V2 Remastered, you will need to destroy a tank by shooting the fuel supply.
A good place to unlock this trophy is during the game's first level. Make your way through the mission until you are on the top of a building and have to shoot a satchel charge that you placed a little earlier to stop a convoy. Once you shoot the satchel, you will unlock the trophy below:
After you shoot the satchel charge, you will have to fight a few soldiers, and then eventually a tank will arrive. At the back of the tank, you will see two fuel supplies with a red cap on top. Hold
to goes into focus mode, and shoot either of the red caps to unlock the trophy.