There are a few reasons why Dr. Cox may touch his nose. It could be a nervous habit, or he could be trying to discretely scratched an itch. However, the most likely reason is that he's using a technique called the pinching test.
The pinching test is used to check for dehydration. To do the test, you pinch the skin on the back of your hand and then release it. If the skin takes longer than normal to snap back into place, it's a sign of dehydration.
Dehydration can cause all sorts of problems, from headaches and dizziness to confusion and fatigue. That's why it's important to stay hydrated, especially in hot weather or when you're exercising.
If you think you might be dehydrated, try the pinching test yourself. If your skin doesn't snap back right away, drink some water and see how you feel after a few minutes.