That depends. If the part that is covered is blocking all light, then that part of the leaf will not undergo photosynthesis. Photosynthesis may continue in other parts of the leaf that are not covered.
This is also partly true even if no light is reaching the leaf. This is because photosynthesis is a two part process; consisting of light-dependant reactions and light-independant reactions. The independant reactions rely on products from the light-dependant reactions, but they can continue with no light as long as the store of stuff made by the light-dependant reactions lasts.