user exit

i want to update one z table from the Service PO, after saving. Hence i require , an user

exit, which will give the details of the service tab , of the PO. I am not able to get any exit, where the details of the

Service tab, of the transaction me22n. Below is the screen of the Service tab of the purchase Order Screen :
Line

DeService numbShort text Quantity Uni Gross priceCr
10 3000001 Sub-Con Recruitment Commissio91 DAY1,249.00 IN
20

3000001 Sub-Con Recruitment Commissio91 DAY1,249.00 IN