z/OS systems have a (1, singular) master catalog. Although there are other methods, the easiest way to determine the name of the master catalog is to use IDCAMS to display information for a dataset known to be cataloged in the master catalog such as SYS1.LINKLIB. Write this IDCAMS control statement.
You will get output like this
NONVSAM ------- SYS1.LINKLIB
IN-CAT --- NONE.OF.YOUR.BUSINESS
The master catalog is NONE.OF.YOUR.BUSINESS.
You can determine the user catalogs by writing this IDCAMS control statement.
The output will be the list of user catalogs.