You can use package manager (pm) over adb shell to list packages:
adb shell pm list packages | sort
and to display where the .apk file is:
adb shell pm path com.king.candycrushsaga
package:/data/app/com.king.candycrushsaga-1/base.apk
And adb pull to download the apk.
adb pull data/app/com.king.candycrushsaga-1/base.apk