Hi Daria,
When we do budgeting for fiscal years, the values get stored in the table BPJA with from the perspective of the Object number of the WBS element. You check the key fields of the table in SE11 transaction.
Simultaneously, the values get stored in the table BPEJ. But this is from the Document number perspective. Every time you do budget, you can see in the status bar that some document being posted. So, the values stored in this table are from the perspective of document number. The key fields of the table in SE11 can explain that.
While BPEJ is for line items, BPBK is for the header document.
And regarding activities, KBUD represents original budget. KBN0 represents budget supplement and KNR0 represent budget return.
Regards,
Manjunadh.