dbname=# SELECT grantee,privilege_type FROM information_schema.role_table_grants WHERE table_name='mytable';

 grantee  | privilege_type 
----------+----------------
 user1    | INSERT
 user1    | SELECT
 user1    | UPDATE
 user1    | DELETE
 user1    | TRUNCATE
 user1    | REFERENCES
 user1    | TRIGGER
 user2    | INSERT
 user2    | SELECT
 user2    | UPDATE
 user2    | DELETE
(11 rows)