[A] In order to punch SQ, open the RFQ against which you want to punch SQ and scroll down to RFQ Summary.
[B] Now click on the yellow button of desired counter party for which you want to punch the SQ.
[C] Now enter the details of SQ received and click on the "Save And Send".
[D] Now in order to create Purchase Order(PO) against this SQ, open the SQ by clicking on "View" as shown below.
[E] You can see the punched SQ, now click on "Other Action" >> Generate PO.