There should be tools that help you appraise gems and art objects. Other than that: int check, maybe investigation or history added depending on situation.
If you require a reason to identify the value of foreign or high value objects, the PHB lists several ways to help. Related tools such as Jeweller's, Glass-Blowing, or other related tools would allow you to add you proficiency bonus to the check. Buying a magnifying glass specifically aids in inspecting close details. Certain backgrounds could apply, such as Guild Artisan or Noble.