1. If you're running a local Mendix app with the default database configured,you can launch DB Viewer in Mendix studio pro and explore the database. In Mendix console > advance setting > DB viewer.
2. if you're running a Mendix app on Mendix cloud-free app, you can't see the database.
3. If you're running a Mendix app on the Mendix license node, you can take database backup & restore in PostgreSQL using pg tools.