Is there any way i can access the object of one client session from another client session?
I'm not sure to get what you're trying to achieve but, according to Server and Client Sessions from the TopLink Developer Guide, you're not supposed to share client session accross multiple threads:
Although client sessions are thread-safe, do not use them to write across multiple threads. Multithread write operations from the same client session can result in errors and a loss of data. For more information, see "Concurrency".
Could you clarify why you would need this?
Unless you have isolated your Entities to the client Session (ClassDescriptor.setIsIsolated) then the ClientSession does not actually hold any entity instances. So unless you have caching disabled all queries against a ClientSession will return the same entity instances.
If you have isolated Entities or are actually using a UnitOfWork then you will have to get the value from the holding UnitOfWork/IsolatedClientSession. It is not advisable to access a UnitOfWork or ClientSession concurrently with multiple threads.