I am able to post to LinkedIn via the API and I get the URN/id of the post returned, but I don't know how to get the actual URL of the post using the returned URN. I cannot find the information anywhere in the API documentation.
In case you have a share or ugcPost, the following URL is valid:
https://www.linkedin.com/embed/feed/update/<urn>
or, for embedded content:
https://www.linkedin.com/feed/update/<urn>
as example:
https://www.linkedin.com/feed/update/urn:li:share:<share-id>
or
https://www.linkedin.com/feed/update/urn:li:ugcPost:<ugc-post-id>
Working link from Test Organizations:
https://www.linkedin.com/feed/update/urn:li:share:6743008621090611200