If you only have the Id (since nevent makes the rest optional) there is no slick magic. Now that this is clear, when you create an nevent include the author so other people don't have this problem. I'd even suggest changing the NIP to make the author required for an nevent.
I should have given more info above. This is in the context of an external web app working with a NIP-21 URI in the format `nostr:nevent1xxxx`. Relay and author metadata are optional so we can't always do the Outbox model bootstrapping sequence magic as we may not even have the author pubkey (although I'll tag nostr:nprofile1qqswuyd9ml6qcxd92h6pleptfrcqucvvjy39vg4wx7mv9wm8kakyujgpypmhxue69uhkx6r0wf6hxtndd94k2erfd3nk2u3wvdhk6w35xs6z7qgwwaehxw309ahx7uewd3hkctcpypmhxue69uhkummnw3ezuetfde6kuer6wasku7nfvuh8xurpvdjj7a0nq40 here just in case as he often has magical solutions to everything nostr :))
I wonder what software like njump.me do to retrieve a note by nevent.
