How is the second equivalence point calculated?

Hint: The equivalence point is defined as the point at which the base added is enough to neutralize the acid to form salt. At the equivalence point the number of moles of acid base are equal.

Complete step by step answer:The acid-base titration is a quantitative method used to determine the concentration of acid or base by neutralizing with the known concentration of acid or base.
The solution which is added of known concentration is known as the titrant and the solution of unknown concentration is known as analyte.
During the titration, the point at which the titrant added is enough to neutralize the analyte solution is known as the equivalence point. At the equivalence point the number of moles of acid is equal to the number of moles of product and as a result salt product is formed along with water.
The first equivalence point is the point of the titration where the first hydrogen ion ${H^ + }$ ion from the initial volume of acid has been neutralized by the base which is used as the titrant.
${H_2}A + O{H^ - } \to {H_2}O + H{A^ - }$
At first equivalence point: 1 mole of acid is reacted with 1 mole of base.
The second equivalence point is the point of titration where the both the hydrogen ion ${H^ + }$ ion from the initial volume of acid has been neutralized by the base which is used as the titrant.
${H_2}A + 2O{H^ - } \to 2{H_2}O + {A^{2 - }}$
At second equivalence point: 1 mole of acid is reacted with 2 mole of base.
Titration curve is shown below.

The volume of strong base required to get the first equivalence point and the volume required to get the second equivalence point is nearly equal.

Note:
You must know that the volume needed to reach each equivalence point is equal and the only difference between each equivalence point is the height of the steep rise.