Unfortunately, I don't know. Also, A lot has happened with the popup system and add to cart and if you replace some code from HikaShop 1.6.0 with some code of the 2.2.2, it's likely that it will get even worst and break the whole page with a Fatal error because the new code is expecting something else to be available somewhere else in HikaShop.
The best I can say is to look in the updatecart function of the components/com_hikashop/controllers/product.php where the add to cart action is processed and which can potentially call the display of the popup, and also look in the file administrator/components/com_hikashop/helpers/cart.php where the popup is initialized.