When using the psql command line, you may list all schema with command \dn.

Connect to the psql command --> psql --u {userName} {DBName} then you can type the below command to check how many schemas are present in the DB

DBName=# \dn

Else you can check the syntax by the below steps easily-

1. After connecting the the DB, press

   DBName=# help
   

You will get the below options:

You are using psql, the command-line interface to PostgreSQL.
Type: \copyright for distribution terms
\h for help with SQL commands
\? for help with psql commands
\g or terminate with semicolon to execute query
\q to quit

Then press

DBName=# \?

You will get all the options very easily.

Beginning On postgres 9.3, One trick you can use in postgres to get the exact sql of informational command (such as \d, \du, \dp, etc) in psql is by using a transaction. Here's how the trick goes. Open one postgres session, then type your command :

begin;
\dn+

While the transaction still running, open another postgres session, and query the pg_stat_activity and you can get the exact sql.

postgres=# select query from pg_stat_activity ;
                                 query                                 
-----------------------------------------------------------------------
 SELECT n.nspname AS "Name",                                          +
   pg_catalog.pg_get_userbyid(n.nspowner) AS "Owner",                 +
   pg_catalog.array_to_string(n.nspacl, E'\n') AS "Access privileges",+
   pg_catalog.obj_description(n.oid, 'pg_namespace') AS "Description" +
 FROM pg_catalog.pg_namespace n                                       +
 WHERE n.nspname !~ '^pg_' AND n.nspname <> 'information_schema'      +
 ORDER BY 1;