Site-wide scripts are usually in a head or footer chunk, but of course every site is custom built so we can’t tell you where it is.
The script you’re referring to seems to be located towards the bottom of the page, so you can try reading through the template and following the chunks to find where it is.
If it really is not in any chunk, it is also possible for a snippet or plugin to register scripts like this to the page. Do you have full permissions (sudo) to the site, or could some chunks be hidden from your account?