How to generate missing values for each employee for each day
You must generate all possible (employee, day) pairs, so you must obtain employees list additionally, not only days list.

The query will be something like

SELECT emp_list.emp_Id, day_list.day, COALESCE(EmpWorkCount.daycount, 0) daycount
FROM ( SELECT 0 day
       UNION ALL
       SELECT 1
       UNION ALL
       SELECT 2
       UNION ALL
       SELECT 3 ) day_list 
JOIN ( SELECT emp_Id FROM EmpWorkCount 
       UNION 
       SELECT emp_Id FROM Emp ) emp_list
LEFT JOIN EmpWorkCount ON day_list.day = EmpWorkCount.day
                      AND emp_list.emp_Id = EmpWorkCount.emp_Id
/* ORDER BY 1, 2 */