Which(been or being)should be used in this sentence; Cognitive psychology is _ used in this book.

Cognitive psychology is being used in this book.
Cognitive psychology has been used in this book.

Here's more on being and been.

Generally:

Being goes with am, is, are, was, were, will be.
Been goes with has, have, had and will have.

Cognitive Psychology has been used in this book

This is when the author wants to state the same at the end of the book.

Cognitive Psychology is being used in this book.

This is when the author wants to mention the same in the beginning of the book,that is in preface.