Here is a script which generates grant queries for a particular table. It omits owner's privileges.
SELECT
format (
'GRANT %s ON TABLE %I.%I TO %I%s;',
string_agg(tg.privilege_type, ', '),
tg.table_schema,
tg.table_name,
tg.grantee,
CASE
WHEN tg.is_grantable = 'YES'
THEN ' WITH GRANT OPTION'
ELSE ''
END
)
FROM information_schema.role_table_grants tg
JOIN pg_tables t ON t.schemaname = tg.table_schema AND t.tablename = tg.table_name
WHERE
tg.table_schema = 'myschema' AND
tg.table_name='mytable' AND
t.tableowner <> tg.grantee
GROUP BY tg.table_schema, tg.table_name, tg.grantee, tg.is_grantable;