Try running a search along the lines of "ISO 9000 training" in Google or one of the other search engines and you will have more reading than you might care for.
Two aspects to consider -
(a) operational style audits where the auditor is a knowledge expert. The task is more about whether the systems are producing a satisfactory product on a peer review basis rather than attention to administrative detail.
(b) straight QA style audit where the auditor is not necessarily a subject expert (and, on occasion, has very little subject knowledge). The task is more aligned to checking if the systems are functioning in the way they were set up and intended to function rather than looking at the intrinsic quality of the end product.
As to books .... either check the local technical bookstore or municipal library. In each case check catalogues ... and then be prepared to sift through a massive quantity of written material.