Why Euro Truck Simulator 2 not using my laptop's GPU?
I figured it out! Actually it was using NVIDIA graphics card (GPU 1). The reason it was not shown in task manager was because the game was minimized at that time. I minimized the game to check performance in task manager, hence it was not shown at that time.
How did I know it using GPU 1 when game is not minimized? :
I pressed Shift Key 5 times accidently, and it minimized game as Sticky Keys notification appeared. While this my task manager was already open and for 1-2 seconds I observed GPU 1 - 3D written against Euro Truck game! It was just vanishing!