Depending on what subscription you have, you can view the history of each record in the right hand sidebar if you expand the record. If you’re on the free version though, you only get to see 2 weeks of revision history. Another option is to add a “Date modified” field set to monitor only the date at which the employee’s job role changes, which will then display the date of whenever the content of that field was last changed. This isn’t an ideal solution though. If employees change their job roles frequently you might just want to add a Date field that you update manually whenever their job role changes. You could at least add an automated email to remind you to do this whenever that field in the record is updated.