You can use collect for this.
SORT it_ekpo BY lifnr.
LOOP AT it_ekpo INTO wa_ekpo.
wa_final-lifnr = wa_ekpo-lifnr. "Vendor
wa_final-total_po_qty = wa_ekpo-menge. "Total Qty
READ TABLE it_stock INTO wa_stock WITH KEY lifnr = wa_final-lifnr.
IF sy-subrc EQ 0.
wa_final-total_stock = wa_stock-total_stock.
ENDIF.
COLLECT wa_final INTO it_final.
ENDLOOP.