query to identify all data types used in postgresql database tables
select data_type, count(*) 
from information_schema.columns 
where table_schema = 'public' 
group by data_type ;


For other schemas just add: or table_schema = 'your_schema_name'.
If this will not satisfy you, you should look in pg_... or information_schema tables.

If you are looking for table information:

select data_type, count(*)
from information_schema.columns
where table_schema = 'public' and table_name = 'your_table_name'
group by data_type ;