Is there a book on MBA HR jobs in which I can study about job details before pursuing it?

No, there is no such book specifically on MBA in HR. For this, you need to join MBA, because the insights of HR is only known by experienced people who have already worked. But, if you want to gain knowledge about HR, then you can take book of Strategic Human Resource Management by oxford university

As far as anyone knows, there is no such job. But, you can ask someone who does that job about how the job is and what are the requirements for it, and later you can decide whether you want to pursue MBA in HR or not.

The job details can not be explained, in a nutshell. You learn the basics in a course and they help you do the job.