Is Zakat obligatory on money donated by a relative to my son to complete his studies, given that this money has reached the Nisab and a Hawl has passed over it? And is it permissible for me to take from this money if I am eligible for Zakat?

Zakat is obligatory on wealth if it reaches the nisab (threshold) and a full lunar year has passed, even if it is designated for specific purposes. The nisab is equivalent to 595 grams of silver.

If the donation was given to you to spend on your son's studies, then the money is yours, and zakat is obligatory upon you. It is not permissible for you to pay zakat to yourself.

If the donation was for the son, then zakat is obligatory upon him, and it is not permissible for him to pay it to you unless you are indebted and cannot find what to repay your debt with, or if the son is not religiously obligated to spend on you.

Scholars indicate that zakat should not be paid to parents or children if the zakat payer is obligated to spend on them, because paying zakat in this case would relieve them of the obligatory maintenance and benefit would accrue back to them.

Two cases are exempted from this: 1. If the father or mother are poor and the son is unable to support them. 2. If the parents or children are among the gharimin (debtors), the mukatebin (those seeking manumission), or the ibn al-sabil (travelers).

If the son needs money for his studies, it appears that he is not obligated to spend on his father unless he has work that suffices him and yields an excess, in which case he must spend on his father from that excess.