Hi Tan,
You can use the table EKKN, EKKO and PRPS to get data Vendor PO, WBS element details and BSEG, BSIK and BSAK.
You can also use the BAPI “BAPI_PROJECT_GETINFO”, then pass these (WBS, activity) in EKKN table to get account assigned purchasing documents. Then get vendor from this and pass in balances table (BSIK, BSAK) to create your report.
Regards
Javed