The principle (in theory) of SGX remote attestation is that you can verify that a specific value (e.g. a cryptographic key) has been produced in an enclave running a specified code. The attestation that this code is running in the enclave is called a 'quote' and is signed with a key unique to that CPU. You can then use Intel's attestation service to verify its a genuine enclave.

There are lots of caveats to this though, and you must trust intel (and also there are privacy issues using intel's service).