We were looking to try and connect chats from one session to another (or even across multiple visits on multiple days). However there does not seem to be any attribute or metric in Explore reporting that shows the "visitor_id" field that exists in the Chat history log. I made a comment on the following article: https://support.zendesk.com/hc/en-us/articles/360022365213?page=2#comment_360006397413 

The feedback I received was that something like this does not exist in Explore and we could set it up so that the chats create tickets in Support. I was told to fill this out to bring it to attention that there is no way to report out on the visitor id that exists in Chat. Also, for what it's worth, our pre chat menu requires users to fill out an email address. However, this email field does not exist in Explore also.

Thanks!