Segmentation Emails - Find which segment a person was sent via activity log

For example, will all the people in Korea that were sent the segmented email show a variant id of 15? Is there a way to match the Variant ID # to a specific segmentation?

No, because more than one segmentation can be used a given email.  It's not a one-to-one characteristic of emails.

You should look at the lead's current segment (or their closest Segment Changed activity, depending on timeframe).

Not a scaleable solution in the slightest, but if it's a small use case and you want to see what they would have seen, and - to Sanford's point re: timeframes - you're looking at segmentations that are relatively stable (i.e. it's unlikely the lead's segmentation has changed) you can also preview the email and view by this specific lead.

If this is something you want to have work to scale as a reference in future, one solution I can think of would be setting up smart campaigns that add people to static lists based on their segmentation positioning at time of sending, providing a static picture of who would have received which combination at that point in time. But again - to Sanford's point re: 1:1 - if you're using multiple segmentations in a single email, the possible combinations start to make this inefficient pretty quickly, so it'd only really be useful in simple use cases.