Can the front facing camera of iPhone 6/iPhone 6 plus achieve the 240 fps slow mo capability? I searched and cannot find information about this. Any help would be appreciated.
Nope. Front facing FaceTime HD camera cannot take video at 240fps. Only the rear iSight camera on the iPhone can do that. You won't find any information about this is because it's understood if that were available the company would have it very well advertised.
As presented on Apple's website, the 240 fps slow-mo is a feature of the iSight camera (i.e. the back camera). The FaceTimeHD (i.e. the front camera) does not have this feature.