This is a very popular way to show off the object’s wireframe. Basically, you want to combine the AO and Wireframe shaders together to show both the shape and polygon structure of the model.
There are quite a few ways to achieve this, but this is the best approach. Take your AO shader and change the Dirt map to Composite map. Now add another layer to the comp and set up an EdgesTx in that layer. This gives you the most flexibility. You can choose the wire color and how to composite it on the base layer. For a basic, traditional look, use black wire color and just reduce the opacity of the second layer to 50%.
