What is the ruling regarding prayers, fasting, and reading the Qur'an for someone who used to practice masturbation, not knowing that it necessitated ghusl, and does not know how many of these he missed, and is there any expiation due from him?

Ejaculation caused by masturbation during a Ramadan (definition) day invalidates the fast according to the majority of jurists. The one who commits this act is obligated to repent and make up the fast. As for expiation (kaffarah (definition)), the more accurate opinion is that it is not obligatory, as it is only definitively established for sexual intercourse, and masturbation cannot be analogized to it. Whoever is unaware of the number of days they missed fasting should rely on what they predominantly believe to be true, and they should frequently seek Allah's forgiveness and acquire religious knowledge.