Help with SQL Query

Please try this:

 
;WITH 
cte_tally10 AS ( 
    SELECT * FROM (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) AS numbers(number) 
), 
cte_tally1000 AS ( 
    SELECT ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) - 1 AS number 
    FROM cte_tally10 c1 CROSS JOIN cte_tally10 c2 CROSS JOIN cte_tally10 c3 
) 
SELECT A.*, ca1.DeliveryDate 
FROM TABLE_A A 
CROSS APPLY ( 
    SELECT MAX(AllDates) AS DeliveryDate 
    FROM ( 
        SELECT TOP (A.NbDays) DATEADD(DAY, t.number, A.JobDate) AS AllDates 
        FROM cte_tally1000 t 
        WHERE 
            t.number BETWEEN 1 AND A.NbDays + 30 AND 
            NOT EXISTS ( 
                SELECT 1 
                FROM Closing_Date CD 
                WHERE CD.Date = DATEADD(DAY, t.number, A.JobDate) 
            ) 
        ORDER BY t.number 
    ) AS derived 
) AS ca1 
 

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I would recommend implementing a true Calendar table and have a boolean column to indicate whether you are closed are not.  It saves a step.  Below is a possible solution that hopefully will help out.

DECLARE @Closing_Date TABLE
(
	[Date]			DATE			NOT NULL,
	[Description]	VARCHAR(500)	NOT NULL
);

INSERT @Closing_Date
(
    [Date],
    [Description]
)
VALUES
	('20200101', 'New Years Day'),
	('20200704', 'Independence Day'),
	('20200701', 'Canada Day'),
	('20200710', 'Closed'),
	('20200711', 'Closed'),
	('20200712', 'Closed'),
	('20201224', 'Christmas Eve'),
	('20201225', 'Christmas Day');

DECLARE @TableA TABLE
(
	JobNo			INT		NOT NULL,
	JobDate			DATE	NOT NULL,
	NBDays			INT		NOT NULL,
	DeliveryDate	DATE	NULL
);

INSERT @TableA
(
    JobNo,
    JobDate,
    NBDays,
    DeliveryDate
)
VALUES
	(1, '04/11/2019', 68, '02/01/2020'),
	(2, '04/15/2020', 56, '08/01/2020'),
	(3, '05/05/2020', 68, '08/01/2020');

WITH cteCalendar AS
(
	SELECT CAST('20190101' AS DATE) AS [Date]
	UNION ALL
	SELECT DATEADD(DAY, 1, [Date])
	FROM cteCalendar
	WHERE [Date] < '20211231'
),
cteClosedCalendar AS
(
	SELECT C.[Date],
		CASE WHEN CD.[Date] IS NOT NULL THEN 1 ELSE 0 END AS IsClosed
	FROM cteCalendar AS C
	LEFT OUTER JOIN @Closing_Date AS CD
		ON C.[Date] = CD.[Date]
),
cteJobCalendar AS
(
	SELECT Job.JobNo,
		Job.JobDate,
		Job.NBDays,
		Job.DeliveryDate,
		C.[Date] AS CalendarDate,
		C.Isclosed,
		ROW_NUMBER() OVER(PARTITION BY Job.JobNo, C.IsClosed ORDER BY C.[Date]) AS DateRowNumber
	FROM @TableA AS Job
	INNER JOIN cteClosedCalendar AS C
		ON Job.JobDate < C.[Date]
)
SELECT cteJobCalendar.JobNo,
	cteJobCalendar.JobDate,
	cteJobCalendar.NBDays,
	cteJobCalendar.DeliveryDate,
	cteJobCalendar.CalendarDate AS ResultDate,
	DATEADD(DAY, cteJobCalendar.NBDays, cteJobCalendar.JobDate) AS CalcResultDate
FROM cteJobCalendar
WHERE cteJobCalendar.IsClosed = 0
	AND cteJobCalendar.DateRowNumber = cteJobCalendar.NBDays
ORDER BY cteJobCalendar.CalendarDate
OPTION (MAXRECURSION 0);

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Creating Tables:
USE Dict
GO
CREATE TABLE Closing_Date ([Date] Date, [Description] NVarChar(200))
GO
CREATE TABLE TABLE_A(JobNo VarChar(3), JobDate Date, NbDays Int, DeliveryDate Date)
GO
INSERT INTO Closing_Date([Date],[Description]) VALUES
('07/01/2020', 'Canada Day'),
('07/10/2020', 'Summer vacation'),
('07/11/2020', 'Summer Vacation'),
('07/12/2020', 'Summer Vacation')
GO
INSERT INTO TABLE_A(JobNo, JobDate, NbDays, DeliveryDate) VALUES
('001', '04/11/2019', 68, '02/01/2020'),
('002', '04/15/2020', 56, '08/01/2020'),
('003', '05/05/2020', 68, '06/01/2020') -- It was changed for test
GO
SELECT * FROM Closing_Date
SELECT * FROM TABLE_A
GO

Calculating:

USE Dict
GO
DECLARE @JobNo VarChar(3), @JobDate Date, @NbDays Int,
@DeliveryDate Date, @CurrentDay Int, @FinishDate Date,
@WorkDays Int
DECLARE cr CURSOR LOCAL FAST_FORWARD READ_ONLY FOR
SELECT * FROM TABLE_A
OPEN cr
WHILE 1=1 BEGIN
      FETCH NEXT FROM cr INTO @JobNo, @JobDate, @NbDays, @DeliveryDate
      IF @@FETCH_STATUS <> 0 BREAK
      SET @CurrentDay = 0
      SET @WorkDays = 0
      WHILE @WorkDays < @NbDays BEGIN
            IF NOT Exists(
                  SELECT NULL FROM Closing_Date
                  WHERE [Date] = DateAdd(day, @CurrentDay, @JobDate)
            ) BEGIN
                  SET @WorkDays += 1
            END
            SET @CurrentDay += 1
      END
      SET @FinishDate = DateAdd(day, @CurrentDay, @JobDate)
      PRINT 'The job No: ['+@JobNo+']'
      PRINT '@JobDate = ' + Cast(@JobDate AS NVarChar)
      PRINT '@CurrentDay = ' + Cast(@CurrentDay AS NVarChar)
      PRINT '@WorkDays = ' + Cast(@WorkDays AS NVarChar)
      PRINT '@DeliveryDate = ' + Cast(@DeliveryDate AS NVarChar)
      PRINT '@FinishDate = ' + Cast(@FinishDate AS NVarChar)
      IF @FinishDate > @DeliveryDate BEGIN
            PRINT 'The job ['+@JobNo+'] will be finished after the Delivery Date:'
      END
      PRINT ' '
END
CLOSE cr
DEALLOCATE cr

Results:

The job No: [001]
@JobDate = 2019-04-11
@CurrentDay = 68
@WorkDays = 68
@DeliveryDate = 2020-02-01
@FinishDate = 2019-06-18
 
The job No: [002]
@JobDate = 2020-04-15
@CurrentDay = 56
@WorkDays = 56
@DeliveryDate = 2020-08-01
@FinishDate = 2020-06-10
 
The job No: [003]
@JobDate = 2020-05-05
@CurrentDay = 72
@WorkDays = 68
@DeliveryDate = 2020-06-01
@FinishDate = 2020-07-16
The job [003] will be finished after the Delivery Date:

Personally I wouldn't use procedural code when you can meet requirements with straight SQL.

Thank you guys, let me see all the answers, sorry for delay. i will come back

If you can post expected results with the sample data you posted, we can post tested SQL.

Scott I had some problems to understand your Cross apply with the select TOP
got some errors

I did test it.  Please let know the specific error(s) you are getting.  The syntax I used should be valid from SQL 2005 on.

hey guys, need your help here :  https://www.experts-exchange.com/questions/29194894/Running-averages-in-a-select-query.html