In order for users to see the All Employees menu under Admin Menu they will need the permission called 'HR People'.
This can be added for you by your manager or any System Owner user by following the steps below:
Search for the employee and go to their profile.
Click Security, then Permissions.
Click Edit Employee Permissions.
Search for HR People and click the eye icon so that it's not crossed out.
Click Save.
You can also add this permission to a role or a post by following the steps in our article on adding permissions.