To view YouTube 3D videos please make sure the video you are trying to watch is 3D, then go to Phone Settings > Display > 3D Settings > Turn on 3D Service Settings > Turn on View Point Setting (View Point 2)
- When you're on the 3D video, turn the device horizontally and you will see a 2D icon on the screen (see image below).
- Tap it to change it to 3D (see image below). You will see it was switched to a 3D icon.
Once this is completed you should be able to see the 3D Video.