Use the ICISite interface ExportTrustedCertificate method and a trusted certificate's ID to retrieve the actual certificate data string from the server.
Signature:
HRESULT ExportTrustedCertificate(
[in] long lID,
[out, retval] BSTR *bstrCertData);
Refer to Site Certificates and Keys Parameters for an illustration of how this and other ICISite methods can be accessed in the Administrator interface.