It depends on the money order and who you've purchased the money order through.
If it's a USPS money order and you lost the receipt to the money order then unfortunately there's nothing that the USPS can do to track whether the money order has been cashed or not or know where the money order is.
If you have the serial number to the money order you can usually track the money order online on the USPS website.
But without either a money order stub, the receipt or the money order serial number then there's no way of tracking the money order.
That's why you should always keep the money order receipt, stub, or serial number in a safe place where you can get to it and know where it is so you can track the money order should it become lost etc.