Find DKIM and DMARC Records?

To query the TXT record for DMARC, you can use:

dig TXT _dmarc.example.org

To query for a particular record for DKIM, you would need to know the selector prefix. You will find it in the s value in an email's DKIM-Signature.

For example:

DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=example.org;
s=google; t=1615461277;
[…]

You would then query it as TXT:

dig TXT google._domainkey.example.org

For DKIM records, if you have received a DKIM-signed email from that domain, look at the DKIM-Signature header line(s).

From the spec:

All DKIM keys are stored in a subdomain named _domainkey. Given a DKIM-Signature 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.

So in this example, you can then run:

dig TXT foo.bar._domainkey.example.com

Credit to andol, whose comment led me to this solution.

You should use +short with dig to get the DMARC record only.

dig +short TXT _dmarc.domain.com