After the Layer 2 solution is released, if you have already minted domains and are wondering how to determine whether the domain is currently on Layer 1 (Ethereum) or Layer 2 (Polygon), there are a couple of methods you may use to identify.
You can view the icon next to your minted domains from the My Domains page.
Click the domain in question.
If the domain is on Layer 1, the URL will begin with: https://opensea.io/assets/
If the domain is on Layer 2, the URL will begin with: https://opensea.io/assets/matic/