Preheat oven to 350 degrees. Spray a 9X13-inch pan with cooking spray.
Using an electric mixer fitted with a paddle attachment, mix together cake mix, pudding mix, eggs, vegetable oil, and milk until well mixed, about 2 minutes. Pour into pan and bake for 40 minutes.
Let cool for 20-30 minutes.
Using a serving fork or straw, poke holes all over cake.
In a medium bowl, mix Jell-O and boiling water until Jell-O is dissolved. Mix in cold water and pour mixture slowly over cake so that it sinks down in holes. Cover with plastic wrap and refrigerate at least 3 hours.
To make whipped topping, place heavy cream in a mixing bowl of an electric mixer and using a whisk attachment, beat on high until soft peaks form. Gradually add in sugar and continue to beat until cream gets thick.
Spread whipped topping on top of cake and top with sliced strawberries.
Notes
Place bowl and whisk attachment for beating cream in the refrigerator to chill before using.