You only need to use the first connection in the linked field to set up your On Demand object.
If you create two NPrinting source connections:
Then create a single linked field based on these connections ie: Country
Simply use SalesDemo as your connection within your On Demand Object. The linked fields draws the data from the second source connection.
The key is to ensure that you setup your linked field correctly as per the following tutorial:
You're welcome, David!
The functionality of linked fields was created to support NPrinting Multi-doc reporting in general.
Multidoc reports can be used within NPrinting Scheduled Distribution and can also be used with On Demand as well as requested.