How to determine the collation of a table in PostgreSQL?
To check for non-default collations on columns, you can use the following query:

select table_schema, 
       table_name, 
       column_name,
       collation_name
from information_schema.columns
where collation_name is not null
order by table_schema,
         table_name,
         ordinal_position;


To find the collation of the database, you need to query pg_database:

select datname, 
       datcollate
from pg_database;


Here are the relevant pages of the PostgreSQL manual:


http://www.postgresql.org/docs/current/static/infoschema-columns.html
http://www.postgresql.org/docs/current/static/infoschema-collations.html
http://www.postgresql.org/docs/current/static/catalog-pg-database.html