Preheat the oven to 350°F (175°C). Thoroughly coat a cookie sheet with nonstick cooking spray so the baked cake can be removed without sticking.
Place the yellow cake mix, nutmeg, cinnamon, and ginger in a large mixing bowl. Whisk until the spices are evenly dispersed and any visible lumps have been broken apart.
Add the eggs and pumpkin purée to the seasoned cake mixture. Stir briefly by hand, then blend with a hand mixer on low speed until the batter becomes smooth and uniform. Avoid excessive mixing, which may introduce too much air.
Transfer the batter to the prepared cookie sheet and spread it into an even layer. Bake for 6–10 minutes, checking at the earliest suggested time. The cake is finished when a toothpick inserted into the center comes out clean.
Remove the baking sheet from the oven and allow the cake to cool completely without taking it off the sheet. Once cooled, cut it with a knife or cookie cutters into pieces sized to fit the serving glasses.
Arrange alternating layers of pumpkin cake pieces and whipped cream inside each glass. Continue layering until the glasses reach the preferred level. For a polished presentation, apply the whipped cream with a piping bag and finish each trifle with a decorative swirl.
Refrigerate the completed trifles until serving time. Present them well chilled.