Please note that you'll get all the relevant information in EBAN,CDHDR & CDPOS tables. You can pass the value of PR no in OBJECTKEY field of the change tables(CDHDR & CDPOS ).One more condition is that ,when you input PR no. in these change tables, then make sure that the number of digits of PR no. should be 10.
Suppose for eg., if your PR no. is 600012 (6 digits), make sure to add 4 more preceding zeroes, so that total will be 10 & then input that value in OBJECTKEY field as 0000600012 .This will satisy the requirement.
Hope things are clear.