I used python script to fetch how many records in production for which each field has data
Some fields can’t be queried but here is the result of the script where each field has corresponding number of records for which there is data
Id = 361344 OwnerId = 361344 IsDeleted = 0 Name = 361344 RecordTypeId = 361344 CreatedDate = 361344 CreatedById = 361344 LastModifiedDate = 361344 LastModifiedById = 361344 SystemModstamp = 361344 LastViewedDate = 0 LastReferencedDate = 0 AQB__Account__c = 361344 AQB__ActivityDateTime__c = 289414 AQB__ActivityDate__c = 291885 AQB__ActivitySummary__c = 34405 AQB__CallDisposition__c = 209642 AQB__CallDurationInSeconds__c = 0 AQB__CallObject__c = 55 AQB__ConfidentialComment__c = 25 AQB__Date__c = 360619 AQB__DurationInMinutes__c = 24 AQB__EndDateTime__c = 28 AQB__EssentialMove__c = 11047 AQB__Followup__c = 19 AQB__IsAllDayEvent__c = 1 AQB__IsPrivate__c = 1 AQB__IsVisibleInSelfService__c = 12 AQB__Location__c = 237 AQB__Opportunity__c = 19196 AQB__OwnerUnit__c = 0 AQB__Priority__c = 2031 AQB__Purpose__c = 352721 AQB__ReportStatus__c = 361344 AQB__ReportSummary__c = 340370 AQB__StartDateTime__c = 289412 AQB__Status__c = 360051 AQB__Stewardship__c = 0 AQB__SubjectAQ__c = 0 AQB__Subject__c = 361260 AQB__Type__c = 356575 AQCV_CONVERSIONId__c = 289378 USYD_owner_name__c = 361344 USYD_Sub_Purpose__c = 10716 Usyd_Account_2__c = 1978 USYD_Event__c = 15949 AQB__CompletedBy__c = 0 flag__c = 173