Is it permissible to purchase books necessary for a student of knowledge from Zakat funds, knowing that he owns two apartments rented out to cover their cost, and has no other source of income besides the allowance from his parents?

If the debt consumes what a student receives in rent, and what his father spends does not meet his needs, then there is no objection to giving him zakat; because he is poor (miskin). As for giving zakat to a student of knowledge, it has conditions: that his knowledge be Shar'i (Islamic legal knowledge) or a tool for it, and that he be poor and needy, not rich, according to the saying of the Prophet, peace and blessings be upon him: "Charity is not permissible for a rich person, nor for one who is strong and healthy," and that earning a livelihood prevents him from seeking knowledge.