Jorgeoa If your domains are set up in your control panel then we're already generating your DKIM hostname and related DNS record. They aren't in your domain list because they are automatically generated and managed by us. We do the same thing for your DMARC and SPF records.
You can see your DKIM records if you query DNS via the dig
command in a shell session, eg:
# replace domain.com with your own domain
dig TXT dkim._domainkey.domain.com
You can also check by looking up "dkim._domainkey.domain.com" in an online tool like https://dnschecker.org/#TXT/ or similar.