Which chapter of seven deadly sins is season 2 episode 3?
I don’t think there is an exact way to pinpoint this, because the manga often is not correlated with anime episodes, and the anime is often abbreviated as to not become a 10,000 episode Naruto. I would say, however that it is around chapter 108-120.
Contrary to the previous answer, it's found here. It comprises of Chapters 113-116.
Wikia pages of anime usually includes episodes and the chapters that they were based on.