You can a list of indexes in your schema from the USER_INDEXES view, but it will not give you the columns used in each index in the USER_INDEXES view. If you want to see the columns used in an index, you can use the USER_IND_COLUMNS view. Here is an example script for you:

SELECT index_name, table_name, column_name

FROM USER_IND_COLUMNS WHERE table_name = 'EMPLOYEES';

INDEX_NAME   TABLE_NAME  COLUMN_NAME

-------------------- ---------------- ----------------

EMP_EMAIL_UK  EMPLOYEES  EMAIL

EMP_EMP_ID_PK  EMPLOYEES  EMPLOYEE_ID

EMP_DEPARTMENT_IX EMPLOYEES  DEPARTMENT_ID

EMP_JOB_IX   EMPLOYEES  JOB_ID

EMP_MANAGER_IX  EMPLOYEES  MANAGER_ID

EMP_NAME_IX  EMPLOYEES  LAST_NAME

EMP_NAME_IX  EMPLOYEES  FIRST_NAME