Design Studio 4.1 does not parse LISTAGG when you use the WITHIN GROUP clause on a DB2 LUW 9.7 connection.
E.g. this gets underlined in red
SELECT workdept, LISTAGG(lastname, ', ') WITHIN GROUP ( ORDER BY lastname ) AS employees FROM emp GROUP BY workdept
This syntax is supported from Fixpack 4 of DB2 LUW. If you manually change the validation to DB2 10.1 or 10.5 then it parses fine