Oracle 21c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
CREATE TABLE employee_tbl (id, name, email_id) AS
  SELECT 1065, 'Abu',  'email1@example.com' FROM DUAL UNION ALL
  SELECT 1066, 'Umar', 'email2@example.com' FROM DUAL
2 rows affected

SELECT JSON_SERIALIZE(
         JSON_OBJECT(
           KEY 'employees' VALUE JSON_ARRAYAGG(
             JSON_OBJECT(
               KEY 'empno' VALUE id,
               KEY 'ename' VALUE name,
               KEY 'job'   VALUE email_id
             )
             ORDER BY id
             RETURNING CLOB
           )
           RETURNING CLOB
         )
         RETURNING CLOB
       ) AS json
FROM   employee_tbl;


JSON


{"employees":[{"empno":1065,"ename":"Abu","job":"email1@example.com"},{"empno":1066,"ename":"Umar","job":"email2@example.com"}]}


DECLARE
  p_json CLOB;
BEGIN
  SELECT JSON_OBJECT(
           KEY 'employees' VALUE JSON_ARRAYAGG(
             JSON_OBJECT(
               KEY 'empno' VALUE id,
               KEY 'ename' VALUE name,
               KEY 'job'   VALUE email_id
             )
             ORDER BY id
             RETURNING CLOB
           )
           RETURNING CLOB
         ) AS json
  INTO   p_json
  FROM   employee_tbl;
  DBMS_OUTPUT.PUT_LINE(p_json);
END;
/
1 rows affected

dbms_output:
{"employees":[{"empno":1065,"ename":"Abu","job":"email1@example.com"},{"empno":1066,"ename":"Umar","job":"email2@example.com"}]}