I've researched a bit regarding your question, and I will share with you what I discovered.

This feature is not enabled by default on every Kubernetes installation and you would need to enable the swagger-ui through the flag enable-swagger-ui and I believe this was what you where looking for.

--enable-swagger-ui      Enables swagger ui on the apiserver at /swagger-ui.

The issue is that I believe it is not enabled for Google Kubernetes engine and the master node in Google Kubernates Engine does not serve any request for this resource and the port appears to be close and since it is managed I believe it cannot be enabled.

However according to documentation the master should expose a series of resources giving you the possibility to access the API documentation and render them with the tool you prefer. This is the case and the following files are available:

• https://master-ip/swagger.json (you can get the master IP running $ kubectl cluster-info)

  {"swagger": "2.0",
  "info": {
  "title": "Kubernetes",
  "version": "v1.9.3"
  },
  "paths": {
  "/api/": {
  "get": { 
  ...
  

• https://master-ip/swaggerapi

  {"swaggerVersion": "1.2",
  "apis": [
  {
  "path": "/version",
  "description": "git code version from which this is built"
  },
  {
  "path": "/apis",
  "description": "get available API versions"
  },
  ...
  

According to this blog post from Kuberntes you could make use of this file:

From kuber-apiserver/swagger.json. This file will have all enabled GroupVersions routes and models and would be most up-to-date file with an specific kube-apiserver. [...] There are numerous tools that works with this spec. For example, you can use the swagger editor to open the spec file and render documentation, as well as generate clients; or you can directly use swagger codegen to generate documentation and clients. The clients this generates will mostly work out of the box--but you will need some support for authorisation and some Kubernetes specific utilities. Use python client as a template to create your own client.