TOSS berries with sugar; let stand 10 min. or until sugar is dissolved. Meanwhile, cut each cake slice diagonally in half; place 1 cake piece on each of 12 dessert plates.
BEAT pudding mix and milk with whisk 2 min. Stir in 1/2 the COOL WHIP.
SPOON 2 Tbsp. berries over each cake piece on plate. Top with pudding mixture and remaining cake pieces, berries and COOL WHIP.