Each Facebook post has a timestamp on the top (it may be something like "Just now", "3 mins" or "Yesterday"). This timestamp contains the link to your post. So, to copy it, simply hover your mouse over the timestamp, right click, then copy link address.
How to Get the Link to Your Facebook Post on Mobile
Using the Facebook app? Then, it's very easy to get the link to your Facebook post. Simply tap Share > More options > Copy to Clipboard.
Now you can simply paste the URL to your Facebook post anywhere you like!