Evenly divide half of the chopped apple pieces among four parfait dishes or tall glasses. Divide yogurt from one 8-oz. container among dishes. Add 2 Tbsp Grape-Nuts to each trifle, then top with layers of remaining yogurt, chopped apple and a sprinkle of Grape-Nuts on top. Refrigerate at least 15-20 minutes before serving to allow cereal to soften slightly.