How to collapse into a single row from multiple rows
You should be able to use a common table expression along with the ROW_NUMBER and LEAD windowing functions to help with this problem.

--demo setup based on your sample data
Declare @T table(DIV VARCHAR(20), LS INT, TT VARCHAR(5), TN INT, LAT DECIMAL(7,3), LONG DECIMAL(7,3), [DATE] DATETIME, ORDER_NUM VARCHAR(30))

INSERT INTO @T(DIV, LS, TT, TN, LAT, LONG, [DATE], ORDER_NUM) VALUES
('BRIDGE',4,'M',1,128.2,186.638, '2/11/2019 17:58', '1004085730'),
('BRIDGE',4,'M',1,128.2,186.638, '2/13/2019 15:22', '1004085755'),
('BRIDGE',4,'M',1,128.2,186.638, '2/17/2019 14:22', '1004104405'),
('CROSS',4,'M',1,170.4,190.2, '2/1/2019 14:22', '1004104405'),
('CROSS',4,'M',1,170.4,190.2, '2/10/2019 14:22', '1004104520'),
('CROSS',4,'M',1,170.4,190.2, '2/17/2019 14:22', '1004104590')

--the query
;WITH CTE
AS (
    SELECT *
        ,ROW_NUMBER() OVER (
            PARTITION BY DIV ORDER BY [DATE] DESC
            ) AS rn
        ,LEAD([date]) OVER (
            PARTITION BY div ORDER BY [date] DESC
            ) AS prev
    FROM @T
    )
SELECT div,ls,tt,tn,lat,long,[date] AS Latest_Test_Date,prev AS Second_Latest_Dte,ORDER_NUM
FROM CTE
WHERE rn = 1




| div    | ls | tt | tn | lat     | long    | Latest_Test_Date        | Second_Latest_Dte       | ORDER_NUM  |
|--------|----|----|----|---------|---------|-------------------------|-------------------------|------------|
| BRIDGE | 4  | M  | 1  | 128.200 | 186.638 | 2019-02-17 14:22:00.000 | 2019-02-13 15:22:00.000 | 1004104405 |
| CROSS  | 4  | M  | 1  | 170.400 | 190.200 | 2019-02-17 14:22:00.000 | 2019-02-10 14:22:00.000 | 1004104590 |




By selecting directly from the common table expresssion
SELECT * FROM CTE

| DIV    | LS | TT | TN | LAT     | LONG    | DATE                    | ORDER_NUM  | rn | prev                    |
|--------|----|----|----|---------|---------|-------------------------|------------|----|-------------------------|
| BRIDGE | 4  | M  | 1  | 128.200 | 186.638 | 2019-02-17 14:22:00.000 | 1004104405 | 1  | 2019-02-13 15:22:00.000 |
| BRIDGE | 4  | M  | 1  | 128.200 | 186.638 | 2019-02-13 15:22:00.000 | 1004085755 | 2  | 2019-02-11 17:58:00.000 |
| BRIDGE | 4  | M  | 1  | 128.200 | 186.638 | 2019-02-11 17:58:00.000 | 1004085730 | 3  | NULL                    |
| CROSS  | 4  | M  | 1  | 170.400 | 190.200 | 2019-02-17 14:22:00.000 | 1004104590 | 1  | 2019-02-10 14:22:00.000 |
| CROSS  | 4  | M  | 1  | 170.400 | 190.200 | 2019-02-10 14:22:00.000 | 1004104520 | 2  | 2019-02-01 14:22:00.000 |
| CROSS  | 4  | M  | 1  | 170.400 | 190.200 | 2019-02-01 14:22:00.000 | 1004104405 | 3  | NULL                    |


you can see that the rn=1 rows are the latest row for each DIV.  The LEAD window function looks to the row just before the latest row for that DIV to pick up the second_latest_date.



Update: based on your comment about wanting to union multiple tables before applying the windowing functions, you could use an inline table expression like this:

;WITH CTE
AS (
    SELECT *
        ,ROW_NUMBER() OVER (
            PARTITION BY DIV ORDER BY [DATE] DESC
            ) AS rn
        ,LEAD([date]) OVER (
            PARTITION BY div ORDER BY [date] DESC
            ) AS prev
    FROM 
        (
        select cols from TableOne
        UNION
        select cols from TableTwo
        ) as t
    )