A circle does not have any vertices. Vertices (plural for "vertex") are corners, or the place where two straight lines come together to form a point. Circles do not have straight lines that come together to form points.
However, circles do have an edge. An edge is defined as the line where the circle ends; that is, it forms the boundary of the shape. In the case of a circle, the length of the edge is the circumference.
For example, squares have vertices, as they have four sides or edges, that come together to form four points.