Hello Kai,
Can you check Help center document :
Overview of Data Sources in Human Resources Management
This has all the data sources listed for the Human resource along with the key figure and characteristic details.
Btw what is the issue with Data source headcount? can you provide further details here?
PS : I checked the report Employee Turnover: Yearly with this report (Underlying data source - HCMPAU01), you have both Employee ID and cost center available.
Another Data source can be Employee Master Data (HCMEMPB).
As an idea, creating new new custom data source based on these data source should work.
Let me know your input.
Regards,
Harshal