How do I find who redeemed my Apple Gift Card?

There is no way to determine who redeemed it. If you purchased it from a retailer that displays them on a rack available for the public to tamper with them, then you were scammed in the store and they failed to protect your purchase. The retailers are well aware of this common scam that has been around for many years. Ironically some of these stores lock up products where they can be stolen from them, but don't seem to have the same feelings when it comes to their customers. In the future, only purchase Gift Cards when they are secured behind a counter. This is true for any Gift Card.

You can contact Apple here. They won't give you any name or Apple ID. You should also contact the Store Manager of where it was purchased or even escalate to their corporate office. They know what happened and they also know you were scammed right in their store.

Contact Apple for support and service - Apple Support