Hello Sakshi,
Is this the link you used to download the ZIP from GitHub? https://github.com/blefebvre/aem-phonegap-kitchen-sink/archive/master.zip
I just tried this link on a Mac and was able to unzip successfully. If you are using Windows you may be running into path length issues. This sample includes all the required plugins [0] which results in some very deep path structures that Windows complains about.
Another option you could explore are the samples over at https://github.com/Adobe-Marketing-Cloud-Apps. In particular https://github.com/Adobe-Marketing-Cloud-Apps/aem-phonegap-starter-kit is a good place to start. This sample doesn't have as many features as the Kitchen Sink example but doesn't include the plugins in the source which should make downloading and unzipping the project on Windows possible. The README for this project will walk you through all the steps required to install the package into AEM. This sample however does require the use of a shell script to customize it which again may not work on Windows. You could skip this step and still install the package to AEM by just leaving the placeholder values.
Anthony
[0] https://github.com/blefebvre/aem-phonegap-kitchen-sink/tree/master/content-dev/src/main/content/jcr_...
