your request sounds confusing. If you need to convert to unicode in application, why do you ask how to make it in Oracle? You should use Java or C++ or Perl or C# or... whatever language/library functionality.
If you need to do that in Oracle you can use CAST function to convert data to NVARCHAR/NCHAR types.
example:
col binary_of_nonunicode newline
select cast( 'nonunicode text' as Nvarchar2(20)) Unicode_text,
dump('nonunicode') binary_of_nonunicode,
dump( cast( 'nonunicode text' as Nvarchar2(20)) ) binary_of_unicode
from dual;