Unfortunately that doesn't show anything. It seems the sponsored guest login is treated differently from Meraki authentication. With a working sponsored guest login setup, going to Network Wide --> Users only tells me that Meraki authentication is not currently in use in this network.
In my case, I have a user working from home who got a sponsored guest authorization email from someone they don't know. The only evidence we have of the request is the email itself, and it doesn't even tell us which building that person was at when they made the request. With a complete lack of auditing, we'll never know if this request was in good faith and we're letting down a client, or if this was a malicious connection attempt.
you can go for each Access Point and in the "current client" part, you see all the active devices with their names and leased IP addresses and also their MAC addresses. But you can not see the clients whom are offline or with unsuccessful connection request.