In short, none! ClearVPN only collects the information necessary to provide you with the VPN service. This includes information related to your account and anonymous network diagnostic reports. That's it.
ClearVPN has a strict no-log policy, which means the app doesn’t collect any information related to the activity of its users: no IP addresses, browsing history, DNS queries, etc. That way, even if for some reason we'd be forced to provide a record of our user’s activities, there would be nothing for us to turn over. That's exactly what you should expect from a VPN with a genuine “no-logs” policy — we've prepared a blog article on what is "no-logs" and why it's important.