Is it obligatory to make up for the days in Ramadan during which one masturbated, for someone who was not praying at the time, and what are the implications of not remembering the number of such days?

Abandoning prayer is a grave sin; indeed, many scholars consider it an act of disbelief that expels one from the faith. It is obligatory to maintain prayer in the future, repent, and make up for all missed prayers. If the number is unknown, one should continue making them up until their obligation is fulfilled.

As for masturbation during the daytime in Ramadan, if it leads to the emission of semen, the fast is invalidated, and making up the day (qada') becomes obligatory without expiation (kaffarah). If no semen is emitted, then no qada' is required. If the number of days to be made up is unknown, one should continue making them up until their obligation is fulfilled. Intentionally breaking the fast during the daytime in Ramadan is among the major sins.