JDownloader 2 does not use a central database of accounts. Instead, it relies on an internal account manager.
A "premium database" typically refers to a shared file—often a org.jdownloader.settings.AccountSettings.accounts.ejs file—that contains a collection of login credentials harvested by others. The "cracked" part suggests that someone has bypassed the need for you to buy your own accounts, providing you with a pre-loaded list of working premium logins. The Reality: Does It Actually Work? jdownloader 2 premium database cracked
You pay a small monthly fee (usually around $3 to $5) to the Debrid service. They maintain massive premium accounts with almost every major file hoster. JDownloader 2 does not use a central database of accounts