Will God forgive someone who masturbates and abandons prayer, despite repeatedly returning to the sin after repentance? And is it possible to know the final total score in an exam through Salatul-Istikhara?

The treatment for obsessive thoughts is to ignore them. Abandoning prayer is one of the gravest sins, and masturbation is forbidden, requiring sincere repentance.

One must hasten to repent sincerely from all sins, for "the one who repents from sin is like one who has no sin."

It is advisable to associate with the righteous, increase the remembrance of Allah, attend gatherings of knowledge, and distance oneself from causes of temptation.

Salat al-Istikhara is performed when intending to do something, to seek ease in what is good, and it has no relation to knowing exam results.