Explanation

Zakat is widely considered the second pillar of Islam after Shahada (declaration of faith). Namaz is a pillar but usually listed as the second or third depending on the enumeration. Fasting (Sawm) and Hajj are other pillars, while Touheed refers to the oneness of God, which is part of belief rather than a pillar itself. Therefore, Zakat is the most likely intended answer for the 'Second Pillar' if Shahada is considered the first.