Well, legends mode tells me the artifact was offered to a goblin, and that goblin settled in the human hamlet of Strengthnations (7 days' travel). Coincidentally I also apprehended a thief who was carrying an artifact stolen from there, so I have one of their treasures. There doesn't seem to be any way for me to send inquiries to Strengthnations though. I could send my diplomat corps (one unarmed dwarf) to initiate contact if I wanted another human caravan I guess, but I don't know if that would bring me new info about my missing artifact.
If your artifact is in Strengthnations, you have a couple of options. One is to raid for it - basically a squad of military dwarves try to sneak in and grab the most valuable things they can find. If there are books and artifacts, they tend to prioritize those, so it might work. However it will likely start a war with the civilization, so be prepared for that.
I am not sure you can request the artifact back, but if you initiate diplomatic contact and they send you a diplomat, you should get some news from them every year, which may include the artifact. I am not sure if known stolen artifacts create missions like kidnapped children though, so you may still have to raid for it.
Alternatively you could retire your fortress, enter adventure mode, and manually go find the thief, steal it back and return it to your fortress. Horrific violence optional.