I just don't get it... Why isn't there something like a GiveMeTheKeyForTheCurrentNode property? Or is there and I'm missing it?

The TreeView has a SelectedItem property that gives you an object reference to the currently selected node (if there is one)

loNode = Thisform.oTree.SelectedItem
IF VARTYPE( loNode ) = [O]
  ?loNode.Key
ENDIF