Hi Analog IT,
Thank you for the detailed explanation of the steps that you have followed as well as the results that you are seeing.
I'm going to start by answering your last question first--and this will also be helpful for the longer scenario that you have given. When you mark a line on a Sales Order as Drop Ship, and then create a PO for that line, you will have a link/relationship created between the Sales Order line and the corresponding line on the Drop Ship PO. You are able to view this relationship in the Lines - Orders tab (on the ribbon) from each of the respective orders. So the answer to one part of your question is that the Lines - Orders tab will show the relationship between the Drop Ship lines on a Sales Order and the lines on the related Drop Ship PO. That relationship (direct line between Order lines) ONLY exists in the case of a Drop Ship.
The longer scenario that you spelled out is one where the goods are being received into and sold out of the in-house/in-company Inventory. It is not a Drop Ship scenario. In this case, we are able to create POs from the Sales Order lines, but there is not a relationship created between these Orders--other than the fact that the same line item is included on both. As such, it is not possible to start with an Order and see the other Order. The closest that I was able to come was to pull up the Sales Order, click into the line in question, and then click on the Lines - LINE - Item Availability by Event button in the ribbon. If the PO was generated on or near the same date as the Sales Order, you may be able to see the two transactions listed together in the Item Availability by Event page, if you view by Day or Week. However, you may see a number of other transactions on this page--depending upon the level of activity--which could make the information less meaningful.
You can also access the Item Availability by Event from the Purchase Order lines in the same manner as from the Sales Order lines.
