-- Oracle  (all_indexes: depending on grants, dba_indexes: for all indexes))
SELECT index_name FROM user_indexes WHERE table_name = 'MY_TABLE';
-- List of indexed columns:
SELECT index_name, column_position, column_name
FROM user_ind_columns         -- or all_ind_columns / dba_ind_columns
WHERE table_name = 'MY_TABLE'  
ORDER BY index_name, column_order;