What is the ruling on selling a club that was bought before repentance with money from forex trading (currency exchange) and abandoning prayer, and is it permissible to benefit from part of its price to buy religious books and donate the rest, and will the doer of that be rewarded for the books bought with this money?

Praise be to Allah for your repentance from abandoning prayer, which is one of the gravest major sins. As for trading via Forex, if you did not avoid the impermissible aspects (mahazeer shar'iyyah) and became certain that your earnings are unlawful, then you must dispose of what you have acquired by distributing it to the poor and needy or for the general welfare of Muslims. You are not obliged to sell the club you bought with this money. You are not permitted to benefit from unlawful money, even by purchasing Islamic books, unless you are in need of these books to learn the obligatory aspects of religion and are poor, unable to purchase them with lawful money. In that case, you will be rewarded for buying them.