your follows and your saved relays are kept in a NIP-02 record:

https://github.com/nostr-protocol/nips/blob/master/02.md

the NIP-02 document doesn't describe how relays are kept, but it's a quoted JSON string in the "content" field that decodes to:

{

"wss://domain1": {"read": true, "write": true},

"wss://domain2": {"read": true, "write": true},

...

}

your follows, meanwhile, are in the "tags" field like:

[

["p", "pubkey1"],

["p", "pubkey2"],

...

]