Where ARC public key is stored? For DKIM it is [selector]._domainkey.example.org. But for ARC? Is it the same as DKIM and holds in TXT query for domain mentioned above?
Quoting from IETF (this is subject to change): "
All ARC-Seal keys are stored in the same subdomain as DKIM keys [RFC6376]: “_domainkey”. Given an ARC-Seal field with a “d=” tag of “example.com” and an “s=” tag of “foo.bar”, the DNS query will be for “foo.bar._domainkey.example.com”.
This is the only information I can find regarding ARC. This is not a standard yet and is still only on draft (which means that it is not sure at all if this is going to be implemented).
I can recommend you to read the above link
Good to read, because this is more up-to-date: https://tools.ietf.org/html/draft-ietf-dmarc-arc-usage-02