To view and edit the slug, you need to be in the Code Editor view.
– Click on the Show more tools button on the upper right corner of the toolbar and click on Code Editor

– Click on the title and the slug/permalink will appear above.

In either Visual or Code Editor, clicking on the title also shows the permalink on the sidebar.

https://gist.github.com/stormwild/d76cfcc7d430c5d29108e86d54dabeb2