If you're looking for your event's URL to share or promote your event you can find it on your Event Home. To get there, go to the Events tab and click on the name of the event you're looking for the URL for. Then you can find the URL on the Event Home underneath the sample Buy Tickets button.
Please note, the below example is for an event that has not sold any tickets yet. If you have already sold tickets the URL will be located below the recent orders field.