Is the gain of a young man who works in a sports club that separates men from women, and plays music during some training sessions, without knowing whether there is exposure of 'awrah, halal or haram?

It is not permissible for the owner of a sports facility to play music, or to allow the uncovering of 'awrah (parts of the body that must be covered), or mixing between men and women. The money earned from renting the place for permissible sports is lawful (halal), and it does not become unlawful (haram) due to the presence of forbidden acts such as music and the uncovering of 'awrah; because the rental agreement pertains to permissible sports, but these forbidden acts must be avoided.