How can I see who is connecting to my app?

You can see see events for individual people connecting and disconnecting - including the source IP - in the connection lifecycle metachannel. The dev console shows all these events, so if you go to the dev console for the app in question you can see events for connections opening and closing, with their details, including the source IP.

Warning: This feature is intended for debugging, e.g. in development with small numbers of connections.

Once the number of new connections exceeds the number of messages per second permitted by the lifecycle channel, new events will be dropped.

So it's not exhaustive — you cannot use this to get a definitive list of everyone who is using your app in a busy production app.

For a definitive record, which will also let you vet (allow or refuse) who can connect to your app on a case by case basis, you use token authentication, which allows you to use your own server as an 'auth server' to gatekeep who can connect to your Ably app.