If a point is a vertex of convex hull
Hint: the point $p$ is a vertex of the convex hall iff there are two half-lines from it such that all points fall inside the angle created by them.

Here is an idea for an algorithm based on this hint:


   Design an algorithm with two variables $q$ and $r$ (input points). The algorithm will examine each of the input points and will update $q$ and $r$ so that all points checked so far fall inside the wedge $\angle qpr$.