This can show all user-defined views in the current database:
\dv
And, this can show all user-defined views in the current database in detail:
\dv+
*There is no way to show all user-defined views in all databases at once.
In addition, this can show all user-defined and system views in the current database:
\dvS
And, this can show all user-defined and system views in the current database in detail:
\dvS+
And, you can show all user-defined and system views in the current database with information_schema.views and pg_proc as shown below:
SELECT table_name FROM information_schema.views;
SELECT viewname FROM pg_views;