PageItems (I presume you mean "graphic line" and not "line" as in line of text) do not have transformReferencePoints. They are associated with layout window objects in the desktop version of InDesign.
On the other hand, if you want to transform your line, you can do so relative to a reference point you would provide as part of the call to the transformation method you are using.
Which version of InDesign Server are you using?
If you want to create a graphic line, you don't need to know where the transform reference point is--it has nothing to do with object creation. You'd do something like this:
//Given a page "myPage"...
var myGraphicLine = myPage.graphicLines.add();
//Set the location of the first point in the line (in points).
myGraphicLine.paths.item(0).pathPoints.item(0).anchor = [72, 72];
//Set the location of the last point in th e line (again, in points):
myGraphicLine.paths.item(0).pathPoints.item(1).anchor = [72, 288];
i use inDesign CS2 Server. I will test the solution from Ole and then yours.