Are you referring to IBM DB2 certification exam (code:-000-730 ).
If so, then i can help a bit. I've completed my DB-2 certification last month.
DB2 is a database engine just like SQL Server or Oracle or MySQL. And for every different OS,they have different variant.
DB2 for Z-OS is for the servers running on Z-os.
So, if he need some study material regarding clearing this exam, then i can upload them for you.
Its not at all difficult to clear the exam. I myself cleared the exam in first attempt and studied only for 4-5 hours.