Fullscreen app unusable due to focus loss i am quite new to the OSX system and having some issues with ElCaptain. 

Basically a fullscreen application (Android Studio in my case) loses the focus and i have to kill it via the task manager in order to get it up and working again.

To reproduce it i just have to open Android Studio. Then open the Genymotion Device manager and then the desktop switches to my main desktop (where non-fullscreen apps are placed). If i switch back to Android Studio again, the input focus is still on the Genymotion windows which is placed in the background. In this case i cannot bring the genymotion window back to foreground again and Android Studio does not accept any input anymore.

Is there any hotkey combination or other trick to get that window back again? I can see a subwindow "Genymotion*" if i "right"click on Android Studio, but its greyed out and i cannot switch to it this way.

Any tips?
You could use a combination of App Expose (4 finger swipe down) and Mission Control ( 4 finger swipe up or F3) to view all possible app windows. Make sure you have these setting enabled.