To determine which network access policy is applied to a particular host, you should look at the Policy Details window. This window provides information about the types of policies applied (such as Network Access, Authentication, Supplicant, etc.), including the profile name, policy name, configuration name, and any settings that make up the configuration.
FortiNAC p 382: "Under Network Access Settings - Policy Name - Name of the Network Access Policy that currently applies to the host."

The exhibit shows a configuration panel where VLAN IDs are specified for different states, such as Default, Registration, and Authentication. When forcing the registration of unknown (rogue) hosts, if an unknown host connects to a port on the switch, the FortiNAC system will move the host to the VLAN designated for Registration. In the exhibit, the VLAN ID for Registration is set to 111, hence the host would be moved to VLAN 111 to undergo the registration process.