Is it possible to send an registration email confirmation to 2 recipients?
Create an Alphanumeric Text custom data field (call it CC Email) in a set of custom fields used for Participants.  Note the name of your set of custom fields.

Add your CC Email field to a Profile. This will allow the registrant to specify a CC email when registering for your event.

Find the table that was created in your database for your custom field set. Assuming your civicrm tables have 'civicrm_' as a prefix, it will be named something like civicrm_value_mycustomfields_#.  This table will have a column for your CC Email field.  

Override the sendMail() function in CRM/Event/BAO/Event.php:

Find the section of code in the sendMail() function that deals with adding CC and BCC emails:

$sendTemplateParams['cc'] = CRM_Utils_Array::value('cc_confirm', $values['event']);
$sendTemplateParams['bcc'] = CRM_Utils_Array::value('bcc_confirm', $values['event']);


After this code, query to see if there is value in your custom CC Email field for the current Participant and add/append the CC Email address.

$query = 'SELECT my_cc_email_field FROM civicrm_value_mycustomfields_# where entity_id ='.$participantId;
$dao = CRM_Core_DAO::executeQuery($query);
if($dao-&gt;fetch()) {
  $ccEmail = $dao-&gt;my_cc_email_field;
  if(is_null($sendTemplateParams['cc'])) $sendTemplateParams['cc'] = $ccEmail;
  else $sendTemplateParams['cc'] .= ', '.$ccEmail;
}