If the mass of the skate bored doubled but the net force on it remained constant, what would happen to the skate bored's acceleration

The skateboard's acceleration would decrease.

The larger the mass of an object, the more force is required to move it.

The skate board's acceleration would decrease. Imagine you are on a skateboard and then you pick up a heavy box on the way. The speed of your skateboard would decrease since the weight on it increased. Hope this helps.