Hi,
To verify SAP connection to BSI TF, report is RPUBTCU0.
To verify SAP connection to BSI TF for BSI Tax Locator, report is RPUTLTU0.
Generally you can also test the connectivity between BSI and SAP when you run payroll.
Payroll will throw an error message as "RFC connection for BSI Tax Factory version is not available".
Thanks,
Ameet