To find out if a freelancer or vendor has been approved, navigate to their profile. If you see a shield by their name with a tick inside it () then they are approved. If you click the shield you can see who has approved them.
The green tick means that person has approved the freelancer and the red cross indicates that the approver has changed his/her mind and therefore disapproved.
You can set a minimum number of supplier approvers in the admin section. Navigate to 'Approvers' and click on the 3 vertical dots to edit approval settings. By default it is set to 'All', meaning that all approvers have to approve the freelancer but you can also set it to 1 or any other number.