When and how should one perform ghusl after masturbating if nothing was discharged, or if a viscous, whitish or yellowish fluid was discharged, or if the fluid was discharged intermittently, or if fluid was discharged without masturbation and one does not know if it is semen or vaginal discharge?

Ghusl (definition) is not obligatory unless semen is discharged. If it is discharged, ghusl becomes obligatory. If the discharge is madhy (pre-seminal fluid), then wudu' is obligatory, and the affected area must be purified. In case of doubt between maniyy (semen) and madhy, one should follow what is clarified in Fatwa (definition) no. 118636. If semen is discharged after a period of time, ghusl becomes obligatory upon its discharge. As for normal vaginal discharge, it is pure but nullifies wudu'. One must strive against the blameworthy habit (masturbation), and assistance can be sought from Fatawa numbers: 122650, 116787, 116663, 114664.