I wanted to know if we can use Geb and spock framework for windows application automation testing? If yes, then please suggest the suitable tools that can be used with Geb & Spock framework for windows application automation testing.
If you mean that you want to test a web application deployed on windows with Spock/Geb, then yes you can!
You can test any web application regardless of its language (php, python, ruby whatever)
Start reading the Geb manual at http://www.gebish.org/
If you mean a normal windows desktop application, then no you cannot.