1. In bowl of electric mixer, combine ricotta cheese, cream cheese, heavy cream and Sweet'N Low; beat at medium speed until blended. Set aside.
2. In small bowl, combine water and coffee granules; stir to dissolve granules. Add mocha extract.
3. Arrange 24 sugar-free vanilla wafers in a baking dish. Drizzle one-half of coffee mixture over wafers. Spread half of cheese mixture evenly over wafers. Repeat layering with remaining 24 wafers, coffee mixture followed by cheese mixture. Sprinkle top of dessert with cocoa.
4. Chill 2 hours or overnight.