Hello everyone, I am truly grateful if anyone gives me any input here. If item fulfilment has multiple package tracking number, is there a way to track what items are associated with each tracking number? We are using FedEx carrier.

NS doesn't track which items are in which package. It's just all the packages in total sum up an Item Fulfillment. You need either some type of WMS. Or a Shipping solution may be sufficient. Checkout ShipHawk or PaceJet. You could also build your own solution with a custom record with few fields in it, or create 1 IF per package.. Don't really know your use case, so can't say more about it.