Is it permissible to donate a portion of one's salary as charity if the employee is sometimes asked to commit a forbidden act for a few minutes, and he is not certain of its prohibition, knowing that most of his time is free and he does not commit anything forbidden? And how can the amount of this portion be determined?

If the forbidden act is rare and incidental, it does not affect the salary, and there is no need to donate anything from it. However, the doer bears the sin of what he has done. Obedience to the manager or anyone else in a forbidden matter is not permissible, for there is no obedience to a creature in disobedience to the Creator. Aishah (may Allah be pleased with her) narrated that the Messenger of Allah (peace and blessings be upon him) said: "Whoever seeks Allah's pleasure, though it incurs people's displeasure, Allah will be pleased with him and will make the people pleased with him. And whoever seeks people's pleasure, though it incurs Allah's displeasure, Allah will be displeased with him and will make the people displeased with him." One must seek forgiveness, repent, and not return to the forbidden act.