You should create an error-handling program in your Oracle database, which you can call it from your every program in the database and Oracle Apex.  Below is an example:

Create a table to log errors:

CREATE TABLE error_log
(
error_code VARCHAR2 (100),
error_msg VARCHAR2 (4000),
date_occurred DATE,
plsql_program_ref VARCHAR2 (100),
username varchar2(30))
/

Create a database procedure:

CREATE OR REPLACE PROCEDURE prc_log_errors (v_error_code IN VARCHAR2,
v_error_msg IN VARCHAR2,
v_plsql_program IN VARCHAR2, v_user in VARCHAR2)
AS
  PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
  INSERT INTO error_log (ERROR_CODE,
  ERROR_MSG,
  DATE_OCCURRED,
  PLSQL_PROGRAM_REF,
  USERNAME)
VALUES (v_error_code,
  v_error_msg,
  SYSDATE,
  v_plsql_program,
  v_user);

COMMIT;
END;
/

You can call the above procedure in every program of Oracle Apex. The following is an example:

EXCEPTION
WHEN OTHERS
THEN
   prc_log_errors (TO_CHAR (SQLCODE), SQLERRM, 
    'page-9 DA-update-emp', :APP_USER);
   RETURN FALSE;

Now, whenever a user reports an error, you will be able to check error details.