Hi,
The dev tools does not help in this case, as the correction is a server side script. If you want, you can add temporary FTP details, and I will try debugging the code directly. That internal function should return the attachment page url, unless there is a 3rd party filter applied to it. I might be able to tell, via debugging that code section.
The second code should go to the functions.php file in your theme/child theme directory. Sorry about that, I forgot to mention. It does nothing though, it’s just a sample on how to get the ID and the links. The post_id and the url variables in the script contain the attachment ID and the image URL. So if the lightbox script has an API, you can use that there, with those variables.