we can not know exactly how much money in the world but we can try to get an estimate I think in the same way we have an estimated world population that is the number of people estimates instead of the right amount. Let's add all the money from every bank in the world, then add an estimate of the amount of money that we do not think is in the bank, then we can add the total available Cryptos multiplying it to their dollar value, we may be near.