If you don't need selection handled differently for different pages, handle DiagramDocument.NodeSelected to get the event raised for any page in the document. Handle DiagramPage.NodeSelected if you need it only for some distinct page.

I hope that helps,
Stoyan

Check the sample project here:
https://mindfusion.eu/_samples/TabbedView_NodeSelected.zip

The event handlers just add a string to ListBox control:

tabbedDiagramView.Document.NodeSelected +=
	(s, e) => lbLog.Items.Add("DiagramDocument.NodeSelected");
tabbedDiagramView.Document.Pages[0].NodeSelected +=
	(s, e) => lbLog.Items.Add("DiagramPage.NodeSelected"); 

If you draw and select nodes on first page you should see both messages logged. If you open a second page and select nodes there, the log will show only document's message, unless you also attach handler to new DiagramPages (e.g. from TabbedDiagramView.PageAdded event).

If you have already attached handlers but can't get them to raise, check if your project doesn't replace the DiagramDocument/Page objects with new instances at some point without attaching handlers to them.

I hope that helps,
Stoyan