What documentation fulfills the requirement for a description of how the sponsor monitored the study and ensured that the study was conducted consistent with the protocol?

Following ICH E3, section 9.6, is one acceptable way to meet
this requirement. The sponsor or applicant should describe the methods
used to oversee the conduct of and reporting of data from clinical
investigations. The sponsor or applicant should also provide a cross reference
to audit-related information for the investigations, as applicable
(e.g., audit certificates).