I took a look at the database documentation, but I didn't see any field that could be used to identify whether SGX is used.
From what I can tell, you can enable SGX in the bios but it can also be software controlled (if you allow that in the bios). You can find more info here: https://software.intel.com/en-us/articles/properly-detecting-intel-software-guard-extensions-in-your-applications
If you have the SGX software installed on SGX enabled systems, you could just report on the software. Alternatively, you could do a file scan for sgx_uae_service.dll or sgx_urts.dll as the above page mentions.
I don't know if there is a registry key that could be used to detect this.