This seems like something that would be better handled in the front-end application, but anyway here is my solution (with create table code borrowed from above)

CREATE TABLE #WO(WO int, RD varchar(10))

INSERT INTO #WO VALUES (122 ,'asas')

INSERT INTO #WO VALUES (123 ,'der')

INSERT INTO #WO VALUES (124 ,'wer3er')

INSERT INTO #WO VALUES (124 ,'rtre')

SELECT WO, CASE WHEN RowCnt > 1 THEN

'(' + CHAR(96 + Row_no) + ') ' + RD

ELSE RD END FROM

(Select * ,

Row_Number() OVER (Partition BY WO ORDER BY WO) as Row_No

FROM #WO) #t1 INNER JOIN (SELECT wo AS Wo1,COUNT(*) AS RowCnt FROM #wo GROUP BY WO) a ON #t1.WO = a.wo1