You can query the SPN using SETSPN -Q

Example: C:\>SETSPN -Q MsSQLSvc/*

To get all the SPN for MS SQL Server in the domain

Note: You can use the SQL Kerberos utility from Microsoft to help you correct the SPN for your instances.

http://www.microsoft.com/en-ca/download/details.aspx?id=39046

This tool will report and give you a CMD file to correct the invalid SPNs. It will also report if your Service Account is not configured to support Delegation