The reporting data model is a dimensional model meant for reporting, and cannot be queried in the way you are attempting. All of the table names and their associated columns are listed in the Facts and Dimensions documentation I linked.
You can only accomplish SELECT tablename FROM pg_tables; from the console CLI in the unlocked underlying database. I don’t recommend running queries from there without Rapid7 Support guidance, as you could easily damage the underlying database.
For more info on the RDM please read this: Understanding the reporting data model: Overview and query design | InsightVM Documentation