SELECT *
FROM ALL_INDEXES -- or DBA_INDEXES or USER_INDEXES
WHERE TABLE_NAME = 'MY_TABLE' AND OWNER = 'MY_OWNER';
-- Index columns
SELECT TABLE_NAME, INDEX_NAME, COLUMN_NAME
FROM DBA_IND_COLUMNS
WHERE TABLE_OWNER = 'MY_OWNER' AND TABLE_NAME = 'MY_TABLE'
ORDER BY TABLE_NAME, COLUMN_POSITION;