PTH is the receipt, PREQUIS  is the Purchase Request. In the data model you'll need to link the receipt to the PO tables and then join to the PO to the PREQUISO table and then link PREQUISO to PREQUIS. 

thank you for your response!!! 

can you please explain how to add this link and where

In the workflow there is the data mode field. If you drill in you'll see the data models. You'll need some knowledge of the tables and how they are linked/joined.

thank you for your response !! i did something else , i created a function with spe script that return PSHNUM and REQUSR from PREQUIS passin PTHNUM as params.

That's another option