All Kubernetes resources are stored centrally in the etcd database and access through the Kubernetes API server. When using Config Maps or Secrets, the data inside them are directly embedded into the resource it self (i.e. unlike ParsistentVolume for example, they do not just reference to the data stored somewhere else). This is also the reason why the size of ConfigMap or Secret is limited.

As such they can be used on all Kubernetes nodes. When you have a Pod which is using them, the ConfigMaps or Secrets will be mapped to the node where the Pod is scheduled. So the files from the ConfigMap or Secret might exist on given node, but that will be just copies of the original ConfigMap or Secret stored centrally in the etcd database.