Application added callObserver to list of VDN. connected event was not captured for list of VDN.Let me know the possible reason for this Issue

1. I don't think this is relevant to your problem but, CallObserver has been deprecated for over 10 years. You should probably use CallListener. See the AgentView sample application as an example.
2. Have you tried monitoring the VDN using the JTAPI Exerciser?

I checked for Agent View App. My problem Is among the list of VDN, few not Monitored.

Could you provide detail on JTAPI Exerciser

"My problem Is among the list of VDN, few not Monitored."

I do not know what you mean by this. Can you explain some more?

You will find the JTAPI Exerciser in the JTAPI SDK in the <SDK>\tools\jtapiex folder. It will let you perform JTAPI actions (create objects & call methods) without writing code. It will also allow you to see JTAPI events that are sent to the application for Observers/Listeners.

Martin