The correct answer is C . The Port Changes view is the correct troubleshooting location when FortiNAC-F changes endpoint network access, such as moving a switch port into a different VLAN. The study guide states that any time FortiNAC-F changes network access for an endpoint, the change is documented in Network > Port Changes . This view shows the date and time of the change, whether a CLI configuration was executed, the reason for the change, the role or access policy that caused it, the port that was changed, and the VLAN the port was changed to.
This directly matches the troubleshooting requirement in the question: the administrator needs to know when the VLAN change happened and why FortiNAC-F made that network access decision. Option A , Security Event view, is used for security-related events, not detailed port-level VLAN-change history. Option B , Reports view, is too broad and not the operational audit trail for a specific access change. Option D , Admin Auditing, tracks administrative actions, but an automatic policy-driven VLAN assignment is documented under Port Changes, not primarily as an admin audit event.