I just want to know whether my application file (.apk) generated by worklight is encrypted or not?
Encoding is not the same as Encrypting, which did you mean? Perhaps you meant Signing?
Worklight does not sign your .apk, nor even generate it
The .apk generation - be it signed or not - is done by Google's ADT
It is the developer's responsibility (= you) to use this tool to produce a signed .apk. http://developer.android.com/tools/publishing/app-signing.html
What you can do regarding encryption in Worklight is enabling the encryptWebResources option in application-descriptor.xml. This will add another layer of protection to your application's contents - the web resources.
The <security> element" in this Information Center topic.