In the Database On Table Row operation, what does the Watermark column enable the On...

The correct answer is To avoid duplicate processing of records in a database.

If a watermark column is provided, the values taken from that column are used to filter the contents of the next poll, so that only rows with a greater watermark value are returned. If an ID column is provided, this component automatically verifies that the same row is not picked twice by concurrent polls.

Mule doc reference : https://docs.mulesoft.com/db-connector/1.8/database-documentation#listener