The definition of average velocity is:

According to this definition, the vector average velocity is obtained by dividing a vector by a scalar. Since the scalar () is always positive, this definition implies that the two vectors ( and ) have the same direction. We would like to apply this definition to find the velocity at point D. Then and in the definition correspond to an interval that spans point D, i.e., with an initial point just before point D and with a final point just after point D.

You indicated that the velocity vector at point D is zero. According to the definition above, this means that the displacement vector for the interval that spans point D is also zero. If so, then the initial and final points for the interval spanning point D must be at the same location. Is this true?