Solution
NI-XNET Database Editor (Classic)
To show the PDUs in the classic NI-XNET Database Editor, enable
Use PDUs in the
Options menu, as shown in the image below.
NI-XNET Database Editor (Preview)
To show the PDUs in the newer NI-XNET Database Editor Preview, click on Show All PDUs in the View menu, as displayed below. Revisiting should show now Hide PDUs (Unless Required)as an option in the View menu.