When we had the skin prick test it was on his arm. They tested for 13 different things. They put a drop of whatever they are testing on the spot then prick it with a needle so it gets in their blood. It hurts. My son cried the whole time and we had to hold his arm down while they did it. Thankfully they were fast! They don't have to consume the foods.
Then they wait about 30min and check back to see if there is any swelling. It's not conclusive, best to have blood test done at the same time. Our skin prick test only showed a big swelling to egg, but the blood test also showed allergy to wheat, oats, and barley, but not as high as egg. Hope that helps!