The related jobs feature rendered jobs based on;
1. Job Categories: If you have assigned various jobs a specific category, then these will be displayed within the “Related jobs” section.
2. Job Tags (If Present): This will depend on whether you have installed the Job Tags plugin. This plugin will add the ability to add tags to your job listings.
Once you assign Tags to your Jobs, jobs with similar tags will show up in the related section of the current job listing.