IBM offers many options for learning about DB2, whether you are a seasoned IBM i developer but perhaps new to SQL, a long-time Database Administrator on another database/platform, or a Systems Administrator needing to understand how DB2 operates within IBM i operating system.
Options include self guided, downloadable presentations and labs, to classroom offerings, to educational oriented conferences.
IBM offers a number of Internet Based self-guided learning opportunities for DB2 for i, including technical white papers.
Another set of great resources to see how DB2 for i compares in functionality to some of the other RDBMS's on the market is a number of available porting guides. These guides are designed for those considering a migration to DB2 for i, and point out at a high level the considerations and tools available to assist.
DB2 family certifications are offered to i programmers and database administrators.