To be able to click on the Add Employment button you will need the permission 'All People', which can be added for you by your manager or a System Owner user by following the steps below:
Go to the employee's profile in Security and click Permissions.
Click Edit Employee Permissions.
Click Filter and then Options.
Select Advanced and click Filter.
Search All People.
Click the eye and pencil icons so they are set to green, then click Save.
The permission can also be added to a role or post by following the steps in our article on adding permissions.