The DB2 client needs to be installed on the JCS server
To download a copy you should be able to look up "DB2 UDB Administration Client" it is an IBM product. This client is a listener that the JCS uses to communicate with your endpoint. Your DB2 administrator should be familiar with the software and should be able to help you configure it to connect to your DB2 instance.
Additionally, open up Connector Xpress -> Provisioning Servers -> Local Provisioning Server, select the DB2 endpoint and right click it.
Under the "choose managing CS" option verify that at least one of your JCS is selected.