The admin of the instance can see the ip addresses of their users, and from that some location can be calculated. But only the admin of your instance can see that, e.g. the admin of lemm.ee cannot see your ip, because you registered on reddthat.com. Of course if a user uses a vpn or tor this ip based location won't be correct. So afaik it's not possible lemmywise, only per instance, and with limitations.
But other location based metrics of instances are available:
- On Lemmy explorer you can filter instances by languages. This should somewhat correlate with the number of users speaking that language.
- On Fediverse Observer Map you can see the physical location of instances. Also this should correlate with the usage from that countries.
These correlations are just my speculations, without any proof.