Your sample indicates that table1 is an exact copy of two columns of table2 - is this really the case?
Here's one way to do what you want, if table1 is restricted to jobs which already exist in it:
SELECT DISTINCT job
INTO #temp
FROM Table1
TRUNCATE TABLE Table1
INSERT INTO Table1 (job, item)
SELECT job, item
FROM Table2 t2
WHERE EXISTS (SELECT 1 FROM #temp t1 WHERE t1.job = t2.job)
DROP TABLE #temp
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden