AIX

Dear Folks,
Please suggest any Open source db2 tool for working with SQL queries

This DbVisualizer - The Universal Database Tool may not be open-source, but it is free and works fine with DB2.
Is this the answer you are looking for? Your question is a bit vague.

What do you mean "work with SQL queries"? To check how effective they are or just to type and execute them?

My DB2 experience is back from v7 and v8, but in first case you should already have db2expln with your DB2 installation. It shows you if you queries do table scans, do use indexes, tell you the DB2-Dollar costs for your statements (the less the better) and so on. It shows it output in ASCII; there is also a tool that comes with the installation that shows this graphical - maybe it is part of the db2cc, I don't remember it, sorry.
For the second case you might want to use your favourite editor that might hopefully have the feature to highlight syntax, especially for SQL. You can then save that file maybe on the box and feed it the db2 command.

Btw. for performance purposes etc. there is a very neat monitor tool available for free:
http://www.db2mon.com