I am trying to set the background contents of a scene to a skybox effect using about array of 6 images.
I have created the array of images in the correct order, I know I need to then use
+ (instancetype) materialPropertyWithContents:(id)contents
SCNScene's "background" property is of the SCNMaterialProperty class. So you can directly set it's contents to an array of 6 images to setup your skybox (see SCNScene.h).
aScene.background.contents = @[@"Right.png", @"Left.png", @"Top.png", @"Bottom.png", @"Back.png", @"Front.png"];
Make sure your 6 images are square and with the same dimensions.