Is it obligatory for someone who knows that there are those who use magic and jinn to spy on him to stop his work, whether it is an obligation or not? And is his intentional performance of this work considered aiding magic and disbelief? And what is the ruling on his doing so forgetfully or ignorantly?

It is not proper to stop permissible acts for fear of devils, as this is from their instigation. We have what repels their evil, such as the Quran. If an act is obligatory, then it is forbidden to abandon it. A person is only held accountable for what their own hands have wrought. Scholars have differed regarding the devil's knowledge of what is in the heart: some believe that he knows what is in the heart by Allah's decree, others believe that he only knows by conjecture and surmise, and yet others believe that he enters a person's heart and knows what they desire.