I am not sure but could it be in "order_done.php" found in: /templates/gk_quark/html/com_virtuemart/cart?
See:
https://support.google.com/adwords/answer/6095947?hl=en&authuser=0 Part 3 in instructions. They advise the page you put the code snippet on is the one your customer sees after a conversion (or in my case a purchase". When inserting the tag, you'll place it on the static portion of the page, found within the <body> section.
Please confirm the above referenced page is the correct page to to do that and if so WHERE I should put that tracking code specifically so as not to break any of the site's function. If this is NOT the correct page to put this code, please refer me to the correct page that the customer would see after making a purchase.