Graphing the point (2,0) would render the graph not a function.
What is a function?
A function is a sequence of ordered pairs in which x does not repeat and has one output. In this graph, we see that none of the points vertically are below each other. That is the reason that the graph is a function. For this graph not to be a function, we could plot the point (2,0) and the graph would not pass the Vertical Line Test (VLT).
Graphing any point in vertical correspondence to one of the points already graphed would make this not a function.
One example of a point that makes it not a function is (2,0).