It is setup for google.com but you'll need to receive a message from Google to see the selector used. It's not possible[1] to establish if domain is DKIM enabled by doing DNS queries without knowing the selector used.
[1] You'd need permissions to enumerate the entire DKIM zone of the domain which you wouldn't have for a random domain and whilst you could by to bruteforce all selector names combinations between 1 and 63 characters long I wouldn't recommend doing so.
[1] You'd need permissions to enumerate the entire DKIM zone of the domain which you wouldn't have for a random domain and whilst you could by to bruteforce all selector names combinations between 1 and 63 characters long I wouldn't recommend doing so.