If you are in ObjC or Swift so that the compiler is pleased with you using the properties or methods SCNFloorfor the link, this link must be of type SCNFloor.
You can do this by casting:
((SCNFloor*)floor.geometry).reflectionFalloffEnd = 10;
(levelFloor.geometry as SCNFloor).reflectionFalloffEnd = 10
, . ( , , ):
let floor = SCNFloor()
floor.reflectionFalloffEnd = 10
floor.reflectivity = 0.5
let floorNode = SCNNode(geometry: floor)
floorNode.position = SCNVector3(x: 0, y: -10.0, z: 0)
scene.rootNode.addChildNode(floorNode)