I reset his password, but it emailed the instructions to him and without knowing an email I can't go further

But his password has been reset, and if he's like me, he used a secondary email to sign up with (IE my main email is [email protected], but I use a different account when I sign up for stuff to avoid spam). And if he's REALLY like me, that secondary email auto-deletes spam messages... So hopefully he's at least a little bit like me and youtube's instructions for resetting his password are now shuffled away in a junk mailbox somewhere.