In a medium bowl, combine the whipped cream cheese, about 3/4 of the chopped onion, half the shredded cheddar cheese (1 cup) and 2 tablespoons of the yellow mustard. Stir well until smooth. Spread the mixture evenly into the bottom of a 6-quart slow cooker insert.
In a non-stick skillet over medium heat, lightly brown the chopped hot dogs. Pour in the Skyline chili from the can. Stir together with the cooked hot dogs. Pour the chili and hot dog mixture over top of the cream cheese layer.
Sprinkle the remaining cheddar cheese (1 cup) on top of the Skyline chili layer. Cover and cook on high power for one hour or low power for two hours. Garnish with the remaining chopped onion and the remaining yellow mustard. Serve with tortilla chips or your favorite dippers.