Create a calendar table first, if you don't have one already like this:

CREATE TABLE #Calendar(Dt DATETIME NOT NULL PRIMARY KEY);
;WITH cte AS
(
	SELECT CAST('20130101' AS DATETIME) AS c 
	UNION ALL
	SELECT DATEADD(dd,1,c) FROM cte 
	WHERE c < '20131231'
)
INSERT INTO #Calendar SELECT c FROM cte OPTION  (MAXRECURSION 0);

SELECT
	c.Dt,
	o.Office_ID
FROM
	#Calendar c
	CROSS JOIN Office_Location o 
WHERE NOT EXISTS
(
	SELECT
		*
	FROM
		Emp_Attendance ea
		INNER JOIN Employee e ON e.Emp_ID = ea.EmpID
	WHERE 
		o.Office_ID = e.Office_ID
		AND ea.Date = c.Dt
);