Hello. I know this is old, but I had to use this and the solution that was posted did not work.
To disable emailing, for me anyway:
/administrator/components/com_hikashop/classes/order.php
Modify within function save() approx line 316 FROM:
if($new) {
$send_email = $this->sendEmailAfterOrderCreation;
$dispatcher->trigger( 'onAfterOrderCreate', array( & $order,&$send_email) );
modify TO:
if($new) {
$send_email = $this->sendEmailAfterOrderCreation = false;
$dispatcher->trigger( 'onAfterOrderCreate', array( & $order,&$send_email) );
Note: Depending on what other modules and plugins that use hikashop are doing, emails can be dispersed from those as well. In my case, Alpha User Points was also sending an email.