Preheat oven to 350ºF and spray a 9x13 inch baking dish with nonstick cooking spray. Drain crushed pineapple, but reserve 1/2 cup of the juice. Prepare cake mix according to package instructions (with oil, eggs, and water), substituting 1/2 cup of the water with the reserved pineapple juice. Add the grated carrots, walnuts, and vanilla, stirring until combined. Pour batter into pan and bake for 30-33 minutes or until cake springs back when you gently press on it. Allow cake to cool completely.

In a stand mixer fitted with the whisk attachment, whip the heavy cream on high until stiff peaks form. Transfer whipped cream to a separate bowl and return bowl to mixer. Switch to the paddle attachment, and beat cream cheese until smooth. Gradually stir in the eggnog, about 1/2 cup at a time, scraping down the sides of the bowl as needed. Once all eggnog has been added, add pudding mix, vanilla, cinnamon, and salt. Beat on high for 2 minutes until mixture is smooth and thickened.

Add about a third of the whipped cream to the bowl and mix thoroughly. Remove bowl from mixer and use a rubber spatula to gently fold in the rest of the whipped cream.

Slice carrot cake into cubes, then layer half of them into the bottom of a clear bowl/trifle dish. Spread half of the eggnog filling on top of the cake. Evenly drizzle caramel sauce over the filling. Layer the remaining half of the cake on top of the caramel, followed by the rest of the eggnog filling. Sprinkle walnuts over the trifle, then drizzle extra caramel over top. Pipe a border of whipped cream dollops and finish with a tiny sprinkle of cinnamon. Refrigerate for at least 4 hours before serving.