Where should the pen holder be placed in the hand in a scientific way of writing? If you want to judge based on hand shape, how should you judge? I usually use a water pen.

The method of holding the pen you mentioned is generally recommended for writing, and it is also relatively scientific. However, I think there is no fixed pattern for holding the pen. There are several ways of holding the pen in Chinese calligraphy, such as holding the pen with five fingers, Four-finger holding, three-finger holding, two-finger holding, etc., suitable for people with different habits and writing styles. So, as long as you feel comfortable writing and writing freely and freely, that's fine.