I have installed odoo 9
I am able to see the opening balance and closing balance at the beginning and after closing the session.
But how can I see the current balance in the draw while using the Point Of Sale?
Going through the point_of_sale module I do not think you can do this. I do not see any setting under the module settings or the general Settings. You will have to resort to a custom solution, that is, modifing the pos xml view to include an element that shows the balance, send the balance to the web_client and modifing the pos javascript side show the value. The field that interests you is last_session_closing_cash and this does not exist in the Javascript side of Odoo POS where everything takes place.
This value can not always be updated though since Odoo POS is designed to operate offline as well. So if you work offline, then this value will be invalid possibly causing you issues.