Is what comes out of a girl considered manī (seminal fluid) or madhī (prostatic fluid), if she thought about something coming out of her, or if it came out normally without languor or relaxation, or if it was madhī that came out with pleasure? And what is meant by "he may not precisely feel its exit"? And is a yellowish-white spot on the underwear considered madhī or discharge?

A person afflicted with waswas (obsessive doubts) must ignore and disregard them. Do not think about what might have come out of you; rather, build upon the principle that nothing has come out until you are certain. If you become certain that something has exited, then verify its characteristics: if it is semen (maniyy), perform ghusl (ritual bath); and if it is prostatic fluid (madhy), perform wudu (ablution) and purify what it has soiled. If you are unsure about the exited substance, then choose and assign it the ruling of whichever of the two you wish. Yellowish discharge is menstruation if it occurs during the period of your regular cycle or is continuous with blood; otherwise, it is impure (najis) and necessitates istinja (cleansing) and wudu for prayer. There is no blame upon you for considering the doubtful discharge as madhy, and your prayers and acts of worship are valid.