Hi Kari,
Strange, You have access to create Invoice - VF01, but, no access to check the split?
See, when you try to create billing document by giving both SO and DO number and execute you will get 2 lines, above you can see log and Split analysis. If you click on the Split you will get the details for split.
If not, create billing and check either in VF02 or VF03. But here system will ask you for the 2 different documents which you would like to compare.
Regards, Sai Krishna.