I don't know how well you know GDL because this requires GDL knowledge.
Let me attach a screenshot of a test I created.
At the User Origin you can see a geometry I created using Slabs. I then saved this as an Object, because it is not possible to save elements as Curtain Wall Junctions (it is possible to save Curtain Wall Frames, Panels and Caps, but not Junctions).
After saving it, I had to open it for editing in the GDL Editor and change its Subtype to "Curtain Wall Junction" (which can be found at General GDL Object > Model Element > Building Element > Curtain Wall Component > Curtain Wall Junction" in the GDL Subtype hierarchy).
You have to change the subtype because only this subtype can be selected in the "Junctions" page of the Curtain Wall Settings Dialog. Then I started placing it at Curtain Wall Frame intersection points (you can place them only when Frames are visible).
From the screenshot, you can see how the geometry of the Junction is placed and rotated compared to its original geometry modeled from Slabs. You can also see how it is mirrored when placing it on the opposite side of the Curtain Wall Reference Plane.
From this point, you would have to define variables for offsetting it in X, Y, and Z directions so as to position it at the exact desired location.
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