I just took a look on my device (Samsung Galaxy Note 10.1) and found my logs in:
\MyProjectName\MyProjectName\Saved\Logs
I have also found that sometimes the engine crashes or hangs before it has a chance to log anything. In this case, try opening the app on your device while it is plugged in, then open a command prompt or terminal and type:
adb logcat -d > my_device_log.txt
This will spit out a device log file that might give you some hints as to what’s happening.
Hope that helps.