code: public void	getWorldRotation(int boneindex, Quaternionf q)
      {
          Bone bone = mBones[boneindex];
  
          if ((bone.Changed & LOCAL_ROT) == LOCAL_ROT)
          {
              calcWorld(bone, mSkeleton.getParentBoneIndex(boneindex));
          }
          bone.WorldMatrix.getUnnormalizedRotation(q);
          q.normalize();
      }
docs: Gets the world location of a bone (relative to hierarchy root).
  <p>
  @param boneindex	zero based index of bone whose rotation is wanted.
  @return world rotation for the designated bone as a quaternion.
  
  @see #setWorldRotation
  @see #setWorldRotations
  @see #setWorldMatrix
  @see GVRSkeleton#setBoneAxis