I think it is custom printed. You could find a high-resolution lattice design (maybe that one, maybe similar) and have it printed on wafer paper by a bakery.
That cake was made by Madison's on Main in Oklahoma. You could ask them how it was done.
I'm not sure how that exact design is done, but have you checked out the new onlays from Marvelous Molds?
Somebody else just asked the same question about this same cake and the smaller design is done with a stencil. I don't remember where someone found it, but check Global Sugar Art. They have nine pages of side cake stencils.