SQL Server 2019

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SET DATEFORMAT dmy;

CREATE TABLE Shift
(
  Empnum varchar(50),
  punchdate date,
  shift decimal(5,1)
);

CREATE TABLE Leave
(
  Empnum varchar(50),
  LeaveDate date,
  leaveFN decimal(5,1),
  LeaveAF decimal(5,1)
);

INSERT INTO Shift (Empnum, punchdate, shift)
VALUES('Test1', '01/09/2020', 1),
('Test1', '03/09/2020', 0.5),
('Test2', '01/09/2020', 1),
('Test2', '02/09/2020', 1)

INSERT INTO Leave(Empnum, LeaveDate, leaveFN, LeaveAF)
VALUES('Test1' , '02/09/2020', 0.5, 0.5),
('Test1', '03/09/2020', 0, 0.5)

;WITH CTE AS
(
    SELECT punchdate AS CurrentDate
    FROM Shift
    UNION ALL
    SELECT LeaveDate As CurrentDate
    FROM Leave
), Emps AS
(
    SELECT EmpNum 
    FROM Shift
    UNION ALL
    SELECT EmpNum
    FROM Leave
)
SELECT c.Empnum, c.CurrentDate, 
  COALESCE(s.shift, 0) shift,
  COALESCE(l.leaveFN, 0) leaveFN,  
  COALESCE(l.leaveAF, 0) leaveAF 
FROM
(
  SELECT DISTINCT cc.CurrentDate, ee.EmpNum
  FROM CTE cc CROSS JOIN Emps ee
) c LEFT JOIN Shift s ON c.CurrentDate = s.punchdate AND c.EmpNum = s.EmpNum
  LEFT JOIN Leave l ON c.CurrentDate = l.LeaveDate AND c.EmpNum = l.EmpNum

Empnum	CurrentDate	shift	leaveFN	leaveAF
Test1	2020-09-01	1.0	0.0	0.0
Test2	2020-09-01	1.0	0.0	0.0
Test1	2020-09-02	0.0	0.5	0.5
Test2	2020-09-02	1.0	0.0	0.0
Test1	2020-09-03	0.5	0.0	0.5
Test2	2020-09-03	0.0	0.0	0.0