Is the Sony FE 35mm F2.8 ZA Lens sharp? This page visually answers that question. Shown above are 100% crops from a lab-captured 35mm f/4.0 test image. Observe the contrast and resolution of these results.
Is the Sony FE 35mm F2.8 ZA Lens set to 35mm f/4.0 sharper than the Sony FE 35mm F1.8 Lens set to 35mm f/1.8? The image quality comparison above also answers that question. Switch between the results to see the sharpness differences between these lenses.