Navigate to the standard Reports tab where you will find a report folder titled Case Split Reports, and two packaged reports: Cases Split by Month and Cases Split by User. 

These reports rely on the Splitter field (csplit__Splitter__c) to be populated when a Case Split occurs. Verify that this field is specified in the Case Split setup under Additional Settings. Definitions of each value can be found in this documentation. If the Splitter field is not defined, or set to "None", the reports will be blank.

If the Splitter field is set to Original Case

If the Splitter field is set to Newly Split Case

If the Splitter field is set to Both

We recommend setting the splitter field value to "Original Case" or "Newly Split Case" to avoid inflating metrics.

These sample reports are provided as-is, and customization is not supported. Further customization can be performed by your Salesforce Administrator or Consulting Partner.