In Banks there are many types of audit like Retail audit, Credit audit and trade finance . All of these are audit parts of Internal audit.
If you are interested in the credit audit then you can read RBI Circular on loan and advances, IRAC norms. credit policy ,
If you are interest in the retail audit of branches then you can read all the RBI circular related to related audit.
If you are interest in the Trade audit then you can read all the RBI circular related to export / import/ inward remittance /letter of credit / bank guarantee /buyer credit