Is the Nikon 135mm f/2D AF DC-Nikkor Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 135mm f/8.0 test image. Observe the contrast and resolution of these results.
Is the Nikon 135mm f/2D AF DC-Nikkor Lens set to 135mm f/8.0 sharper than the Sigma 135mm f/1.8 DG HSM Art Lens set to 135mm f/5.6? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.