The SQL Assist feature provides auto-completion of database object names and SQL commands and other keywords in queries.

To perform some object name auto-complete, press Ctrl+Space or right-click the required place in the query and click SQL Assist on the context menu. DBeaver searches for potentially suitable objects in already loaded database metadata and in the database system tables.

When you start typing an SQL keyword in a statement, DBeaver offers auto-complete options as well.
Another auto-complete function is search for completion only within already entered identifiers - press Ctrl+Shift+Space.