What is the sum of the measures of the exterior angles of a nonagon?

360 degrees. This is true for all convex polygons

The sum of the exterior angles of any polygon is 360 degrees. Therefore to find the measure of one exterior angle of any regular (all angles are congruent) polygon, divide 360 by the number of angles. In the case of a regular nonagon, the measure of one exterior angle is 40 degrees: 360 / 9 = 40 degrees.