Can someone help on how to extract a list from nickserv of all registered users please?

You don't.

Let me know how to get all the names and phone numbers of everyone ever registered to Facebook. I heard that's a thing now.

It's technically possible to get all the accounts infos from facebook, it's not even possible technically to do what he is asking for..
And with a big bag of money the feat with facebook is not so impossible!

Not possible? You can see all registered nicks with one single command, at least on anope. Only catch is you have to be a services admin.

Depending on the services used.

Anope for example has "LIST" that will list all registered nicknames which are not set private. Also the Services Admins can obviously list even the private nicknames.

For once I thought its the moderator's responsibility to check the registered users.