Approximately how much surface area does this organ cover

Skin is the largest organ and covers a surface area of 20 square feet.

Explanation:

Skin has three layers the epidermis, the dermis and the hypodermis. the epidermis is the outermost layer and provides a water-proof barrier. The dermis contains hair follicles, connective tissue and sweat glands. The hypodermis is the subcutaneous deeper layer made up of connective tissue and fat.

answer: i would say the brain but it seem that you have a brain.