How to check the value of NLS related values like national character set or NLS_NCHAR_CHARACTERSET?

SQL> select value from nls_database_parameters where parameter='NLS_NCHAR_CHARACTERSET';

VALUE
----------------------------------------
AL16UTF16

SQL> select value$ from sys.props$ where name='NLS_NCHAR_CHARACTERSET';

VALUE$
--------------------------------------------------------------------------------
AL16UTF16

SQL> select property_value from database_properties where property_name
='NLS_NCHAR_CHARACTERSET';

PROPERTY_VALUE
--------------------------------------------------------------------------------
AL16UTF16

References

What is national character set / NLS_NCHAR_CHARACTERSET?