What is the ruling on prayers, fasting, and reading the Quran if dry semen is found on clothes, and the time of its emission is unknown, knowing that it might have been emitted two days ago, for example, from the last ghusl?

One must repeat the prayers that are certainly known to have been performed after a wet dream. It is recommended to repeat the prayers where there is a possibility they were performed after it. So, whoever sees semen on their clothes or bedding must perform ghusl (ritual bath) and repeat every prayer that is certainly known to have been performed after the wet dream. As for fasting, a wet dream does not invalidate it. There is no sin in reciting the Quran for a person in a state of janabah (major ritual impurity) who forgot.