On the Juvio website, navigate to the HoN Reborn Play page and select Inventory to view all items associated with your account.

In HoN Reborn, you can view your collection by opening your in-game profile.

This is intentional. A Juvio Marketplace is coming soon, allowing players to buy and sell items with other players. Owning multiple copies means you can sell duplicates and use the Jade you earn to purchase other skins on the marketplace.