WordPress uses a naming pattern that determines what template gets used to display a certain kind of content.
In your case, all you need to do is create a template file with a standard loop and name it single-job_opening.php. This will ensure that this file gets loaded when the user views a single job opening post. You can find out more about this here: http://codex.wordpress.org/Template_Hierarchy
I recommend that you use the Debug Bar Plugin (http://wordpress.org/extend/plugins/debug-bar/) when running into similar problems in the future. Not only will it tell what template is loaded on what page, but it also gives you an indication of what content type is loaded.