Which of the four skills English language is called natural skills?

There's no concept of "natural skills" when it comes to English language skills. The four skills are:

* Reading: Understanding written text.

* Writing: Producing written text.

* Speaking: Communicating verbally.

* Listening: Understanding spoken language.

All four of these skills require learning and practice. While some people may have a natural predisposition towards one skill or another, everyone needs to develop all four skills to achieve fluency in English.