There is also a possibility in the Unity programmer exam that you will come across the odd question on shaders to establish how much you know with regard to creating shaders or knowing what different shaders can create. Learning about shaders is another book in itself, and it's also unlikely when you sit your exam that the majority of it will be devoted to shaders. Hence, if you don't know how to write shaders, do not concern yourself with the coding and focus more on the general practice and functions used. For example, a cel-shaded toon in an environment or custom post-processing effect could be achieved by using functions such as Camera.depthTextureModeto calculate the depth of a scene.
Knowing that these functions and methodologies exist will give you a better chance at answering them and, if you need more information on shaders in general, refer to the Packt book entitledUnity 2018 Shaders and Effects Cookbook - Third...