A Job is the parent folder for all related tasks, documents, discussions & designs for a customers project. The user privilege to delete a Job therefore has the potential to delete ALL Jobs in the database. The privileges are therefore tightly controlled to ensure a user doesn't unintentionally delete more than they were expecting. A Job cannot be undeleted so you will permanently lose all data contained in that Job.
Note: Deleting a Job does NOT delete any Impact designs associated with the contents of that Job
If you already have the user privileges to delete a Job, you can do this in the same way you do for tasks. If the delete action is inactive (greyed out) then you do not have the privileges. You will need to contact your administrator to delete the Job or request permission to do this.