I am Making a lemon dessert calls for one pint heavy cream can I use cool whip?

If the heavy cream is used for a topping only, I guess you could use Cool Whip, but you'd always have better results with whipping the heavy cream yourself. Without seeing the recipe, I would stay away from using Cool Whip as an ingredient that gets mixed into other ingredients. There are plenty of recipes on the internet if you really want to use Cool Whip.