Query for all the Postgres configuration parameters‘ current values?
SHOW ALL

The SHOW ALL command displays the current setting of run-time parameters in 3 columns.

SHOW ALL ;




pg_settings

The pg_settings view shows the same items as SHOW ALL but with additional details, across 17 columns versus 3 columns.

TABLE pg_settings ;




pg_file_settings

To read what is stored in the postgresql.conf file itself, use the view pg_file_settings. 

If freshly written, this file will hold values that may not yet be in effect within the Postgres server. After writing, the settings must be loaded in one of various ways including a server restart.

TABLE pg_file_settings ;




Admin tool

Your databased-administration tool may display these settings.

For example, in pgAdmin 4, choose the cluster name (the Postgres installation) in the navigation panel, click the Dashboard tab, and in a list bottom panel titled Server activity, click the Configuration tab to see a list of your settings.



Writing

By the way… For info about writing these settings with ALTER SYSTEM commands, see my Answer on another Question, How to edit postgresql.conf with pgAdmin 4?.