Is the prayer valid if one doubts the emission of semen, and what is the ruling on its recurrence?

There are several scenarios for wetness:

1. If you are certain it is maniyy (seminal fluid), then you must perform ghusl (ritual bath) and re-pray the prayers you performed after finding the wetness and before performing ghusl. This is the view of the majority of scholars. However, if it exited while awake and without lust, then according to the majority of scholars, ghusl is not obligatory; rather, wudu' (ablution) suffices.

2. If you are certain it is madhiy (prostatic fluid), your prayer is valid if you wash what it touched, perform wudu', and pray in clean clothes.

3. If you are unaware of the nature of the wetness: If you wish, you may consider it maniyy, perform ghusl, and re-pray the prayers. If you wish, you may consider it madhiy, and your prayer will be valid after washing the impurity, performing wudu', and praying in clean clothes. This is the detailed explanation of the Shafi'i school.