How to access apex data from sqlplus?
Table person is situated in schema assigned to your apex workspace. You can go to APEX IDE to the section SQL Workshop -> Object Browser, schema name will be displayed in the top right part of the page. Or you can execute query:

select owner from all_tables
where table_name = 'PERSON';


You will get names of all users that have table with such name.
After that you need to use this name in your query:

select * from schema_name.person