You can easily see who's connected by adding the OpenVPN-widgets to your dashbard. ("Configure Widgets", top of the page, next to the search field.).
That, however, will only list the address the client is connecting from, not which internal VPN-address it has.
I'm sure there's a better way to do this, but you can see which certificate is given which IP by:
sudo cat /etc/openvpn/<name of vpn>-ipp.txt
That file is updated with new ip's as clients with different certificates connect for the first time.
I think you can edit that file too if you want to hand out specific addresses to specific clients/certificates.
::Trym