You can see these changes by creating an Insight report built on the Salary Approval History (Personnel) view. You can add columns such as:
Person Reference
Salary
Effective Date
Approval Date
Approval Id
Transaction Type
Username
Reference And Description
The Transaction Type column will show A, C, or R where:
A - Approved
R- Rejected
C - Created
The Username column will show who actioned the above.