Most of the time the default location differs based on the operating system and sometimes depends on the version also the location may change, and also maybe depend on how you install the server.
To get the location of postgresql.conf
Execute the query show config_file; will give you the location of the conf file
psql -U postgres -c 'SHOW config_file'
Run show config_file from non-default user
vignesh=> SHOW config_file; ERROR: must be superuser or a member of pg_read_all_settings to examine "config_file"
pg_read_all_settingsRole : pg_read_all_settings : Read all configuration variables, even those normally visible only to superusers.
Grant Role to the non-default user
ubuntu@ip-172-31-12-90:~$ psql -U postgres psql (10.12 (Ubuntu 10.12-0ubuntu0.18.04.1)) postgres=# GRANT pg_read_all_settings TO vignesh;
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