is there an info on how much XYM is held on Binance?
As far as I know there is no official info. Since Binance uses one XEM deposit address for all accounts (the assignment happens on the basis of the provided message), I would say they also use one XYM address. Based on the
richlist I would assume that one of the top 3 addresses belongs to Binance and therefore you can estimate how many XYM are on Binance.