If you are working with an ENS library, your library will automatically find the ENS deployment you need. If for whatever reason, you need to interact with ENS directly, details for the currently supported deployments are detailed here.
The ENS registry is deployed at 0x00000000000C2E074eC69A0dFb2997BA6C7d2e1e. This same address is used across Mainnet, Ropsten, Rinkeby and Goerli.
On mainnet, the following registrars are deployed: