Domain names are not SPL tokens, however, they can be tokenized in NFTs that follow the Metaplex standard. It's only recommended to tokenize your domain if you want to resell your domain on an NFT market place like Magic Eden or Hyperspace.

The smart contract handling the tokenization of domain names can be found here: Name tokenizer

JS example

To retrieve all the tokenized domain names

import { retrieveNfts } from "@bonfida/spl-name-service";

// nfts is of type PublicKey[] and contains all the mints of the tokenized domain names
const nfts = await retrieveNfts(connection);

To retrieve the owner of the NFT that represent a tokenized domain name

import { retrieveNftOwner } from "@bonfida/spl-name-service";

const owner = await retrieveNftOwner(connection, nameKey);