You're most welcome.
From what I checked in the code, it is quite complicated to show a specific field value in the email because each of the different types of custom fields also needs to use a different way to retrieve the custom field value.
If you would like to set to use this registration type "Require user confirmation and admin approval", it will be involved the following core files (confirmationUserEmail method), what you need to do is get the newly registered user id from the method.
For example:
// current new register user id
$userId = 100;
// Get this user profile obj data
$userData = ES::user($userId);
// Get a specific custom field value, the URL is the field's unique key
$customField = $userData->getFieldValue('URL');
// You can test the result using this echo php function and see whether it returns the string or not
// because not all the custom field will return you as a string, if the value return to an array then need to use different way to show to the string
echo $customField;exit;
JoomlaFolder/components/com_easysocial/controllers/registration.php (confirmationUserEmail method)
Once you got the custom field value, then you need to pass this custom field value into $params array, so you can pass this variable to the email template file to populate your custom field value.
JoomlaFolder/components/com_easysocial/themes/wireframe/emails/registration/moderator.approvals.php