Spray 2 egg-shaped gelatin molds with cooking spray. Firmly snap the molds together.
Pour gelatin mix in a large heatproof glass measuring cup with a spout; stir in boiling water until gelatin has dissolved.
Slowly pour gelatin into prepared molds.
Refrigerate molds until gelatin has set, about 3 hours.
Unsnap the molds and remove the gelatin eggs; cut each egg in half lengthwise with a sharp paring knife.
Mix whipped topping and instant vanilla pudding mix in a bowl until smooth. Scoop the pudding mixture into a piping bag or plastic bag with a snipped corner.
Pipe about 1 tablespoon of filling into the middle of each egg half for the "yolk."
Sprinkle decorating sugar over each yolk. Chill until ready to serve.