You can’t. Carrara’s specularity is controlled in the shader of the object, not the light. This is a fundamental difference in Poser/DS and most of the rest of the 3D world…
If you have PRO you can render out separate Multi-Pass layers for Diffuse and Specularity.
HDRI / Image-based Lighting (IBL) creates non-directional light without specularity. (any of the Global Illumination options on their own generally do not create specularity, I believe)
You can control specularity in each shader. It is a 2-channel control the first called HIGHLIGHT which controls the color and pattern and uses the UV map (if you have a specular map put it here).... The second channel is called SHININESS and it is a single value (best controlled with a VALUE 0-100 shader) that focuses the specularity according to the angle of the light. Lower numbers spread the specularity across the object, higher values focus the specularity to a narrow angle…. I have a video tutorial on my website called “Creating Skin Specularity” or similar… Link to my site is in my sig below…