Google Kubernetes Engine is a managed service and does not allow you to interact with the master node [1].
Since the nodes are run on GCE, You are able to connect to individual nodes of your cluster thought their individual IP’s
just like you would connect to an instance using putty [2].
[1] https://cloud.google.com/kubernetes-engine/docs/concepts/cluster-architecture#master_api
[2] https://cloud.google.com/compute/docs/instances/connecting-advanced#thirdpartytools