How to show progressbar in App store during installation?
There should be a progress bar underneath the Launchpad dock icon.
If you removed Launchpad from your dock, open it through Spotlight, then search for the icon of the app you are installing (which in your case would be Xcode). There should be a progress bar and further status information on it.
Go to the « Purchased » tab of the Mac App Store. There will be a progress bar.