Under "Tools" on the right, select "Permalink." That will cause it to appear above the title of the item:
There should be a "Abstract/Details" tab above the document. Click it, then scroll down to the bottom of the page where you will find the "Document URL" field:
Between "Published by" and "Page Count" in the item details, you should find "Stable URL:"
Next to the title of the item there should be an "Action" button. One of its options is "Link to this page." Selecting it will cause a pop-up to appear:
Between "Playlist" and "Deselect item" under the description, you should find "Embed/Link." Selecting it will cause a pop-up to appear: