How to retrieve DDL from Database?

DBMS_METADATA package will work for tables, indexes, views, packages, functions, procedures, triggers, synonyms, and types. 

DBMS_METADATA.GET_DDL (object_type, name, schema)

DBMS_METADATA.GET_XML (object_type, name, schema)

SELECT DBMS_METADATA.GET_DDL (‘TABLE’, ‘EMP’, ‘SCOTT’) from dual;