For the officially supported databases, I'd recommend referring to the Joget documentation. I have not used DB2 specifically with Joget but try using the custom datasource option in the list builder to connect to the DB2 database and see how it goes from there. This may allow you to establish a connection and retrieve the file information you need.

Go to datalist builder → Data → You can choose Database SQL Query / Database wizard (Both these options support custom datasource option other than your default database) → You need to enter the connection string and Driver details. 

If you encounter any issues connecting via the custom datasource option, consider developing a custom plugin for DB2 integration. This approach, while more involved, would allow you to create a tailored solution for seamlessly connecting Joget to your DB2 database.

Hope this helps.