Can you use the baking soda you have in my fridge to bake cookies?

It is not recommended. The soda in the fridge has absorbed a lot of different odors and tastes that will affect your baking. The moisture in the air can also react with and decrease its leavening power.

You can test the baking powders potency by taking a spoonful and mixing with a bit of hot water or vinegar. If it bubbles, the soda is still active, but that doesn't get rid of the flavors it has absorbed in the fridge.