How to track an ip address on deviantart?

Not possible. Since every client is connected towards DeviantArt itself, and never to each other. No data is exchanged between users.

Assuming you did NOT intend to use this information for illicit reasons:

You could create your own site that collects user data (such as IP addresses) and send a link to the user you want to collect data from. Just make sure only that user have access to it, otherwise you won't know who is who.