In a separate bowl, add in cinnamon, nutmeg, granulated and brown sugar and give it a whisk. This will help prevent your spices from lumping up. Add in the eggs, eggnog, and milk. Stir until combined.
Spray an 9 ½ x 9 ½ x 2 casserole dish with nonstick cooking spray. place the cake donut slices in the dish. Pour the custard over top and give the donuts a stir to make sure they're all covered.
Cover with plastic wrap and chill in the fridge for 2 ½ hours to overnight.
Preheat oven to 350 degrees.
Remove plastic wrap and place in the oven for 1 hour 15 minutes to 1 hour 30 minutes. Take a peak at the bread pudding. If there is still liquid, it needs a bit longer. Remove from the oven and let cool for 10 minutes.
In a small bowl, add in the powdered sugar and eggnog. Whisk until the glaze is smooth.
Pour over the donut bread pudding.
Place in the fridge for about an hour. Cut and serve.