SELECT value$ FROM sys.props$ WHERE name = 'NLS_CHARACTERSET' ;
SELECT * FROM NLS_DATABASE_PARAMETERS

select owner, table_name, column_name
     from dba_tab_columns
    where (data_type = 'NCHAR' or
            data_type = 'NVARCHAR2' or
            data_type = 'NCLOB') and
            owner != 'SYS' and
            owner != 'SYSTEM';