Finding the URL to be used to check if plugin is installed with a theme

This are not url’s. They are paths. So disqus-comment-system is the folder of the plugin and disqus.php the “init” php file. Every plugin has more or less the same structure. Install your desired plugin and check it’s file structure inside plugin folder of WP.

More: https://codex.wordpress.org/Function_Reference/is_plugin_active