Move oven rack to middle position. Heat oven to 350°F
Beat cake mix and 1 1/4 cups cold water in extra-large glass or metal bowl with electric mixer on low speed 30 seconds; beat on medium speed 1 minute. Pour into 2 ungreased loaf pans, 9x5x3 inches, or 3 ungreased loaf pans, 8 1/2x4 1/2x2 1/2 inches.
Bake 9-inch pans 35 to 45 minutes, 8 1/2-inch pans 28 to 38 minutes, or until top is dark golden brown and cracks feel very dry and not sticky. Do not underbake. Immediately turn each pan on its side on heatproof surface and let rest until completely cool. Run knife around edges; remove from pans.
Line each same loaf pan with plastic wrap, allowing wrap to extend over edges. Place raspberries, sugar and jam in food processor; cover and process, using 3 quick on-and-off motions, until coarsely chopped. Cut each loaf cake horizontally into 4 slices, using serrated or electric knife. Place 1 slice in bottom of each pan; spread 3 tablespoons of the raspberry mixture over each. Top with another slice cake. Repeat with remaining raspberry mixture and cake slices. Cover with plastic wrap and refrigerate at least 2 hours until chilled.
To remove loaves easily from pans, place serving plate upside down on top of pan; turn pan upside down onto plate. Remove pan and plastic wrap. Cut each loaf crosswise into 8 slices, using serrated or electric knife. Serve with whipped topping and blueberries.