Hi Dipak,
You have to fulfill below condition to trigger event handler in your purchase order acknowlegement. Check below conditions and create a new PO, It should trigger event handler if everything fulfills.
CHECK <ls_xekpo>-loekz <> 'L'. - Deletion Indicator should not be there for PO line item
CHECK <ls_xekko>-bsart = 'NB'. PO Document type should be NB
CHECK <ls_xekko>-ekorg = '0001'. Purchase Org should be 0001
CHECK <ls_xekpo>-pstyp = 0. Item Category should be "0 - Standard".
CHECK <ls_xekpo>-menge > 0. Quantity should be greater than zero.
Show the screen of your PO, if it couldn't trigger.
Regards
GGOPII