What should I do with the money I found in my pants, as I don't know if it belongs to me or to the hall where I work?

You must investigate the source of the money. If it becomes clear that it belongs to the prayer hall where you work, you are obliged to pay it to them. However, if this is not clear, then the default is that you are absolved, and the money in your possession is your property. This is based on the jurisprudential principle: "Certainty is not removed by doubt," and that the default for what is in a Muslim's possession is that it belongs to him if he claims it.