The answer may depend upon what you mean by "enabled". If you mean the system has been provisioned and ready to be managed, look at the Class AMT_SetupAndConfigurationService specifically the field ProvisioningState.
If you arereferring to the manageability mode(Intel AMT, ASF, or None), this will need to be done locally at the system. You canread section B20 of the Developer's Guide to the Sample Setup andConfiguration Application to see the APIs available.
The ZTCLocalAgent source provided with the SDK (while based on the old EOI interface)does demonstrate how to determine the state in both situations.