Через openvpn-status.log:

# cat openvpn-status.log | grep 10.8.*
10.8.0.18,tst-svm-web,94.4.21.11:1194,Sat Jun 8 10:01:02 2019
10.8.0.10,note-tst,192.168.1.1:35510,Sat Jun 8 10:01:22 2019

Через консоль (предварительно прописав строку в server.conf)

# echo "management localhost 7505" >> /etc/openvpn/server.conf

# systemctl restart openvpn@server
# systemctl status openvpn@server

и соединившись по telnet/nc:

# telnet 127.1 7505
status
OpenVPN CLIENT LIST
Updated,Sat Jun  8 10:20:20 2019
Common Name,Real Address,Bytes Received,Bytes Sent,Connected Since
tst-svm-web,94.4.21.11:1194,37268,41775,Sat Jun  8 09:57:54 2019
note-tst,192.168.1.1:54486,9973,5094,Sat Jun  8 10:23:00 2019
ROUTING TABLE
Virtual Address,Common Name,Real Address,Last Ref
10.8.0.18,tst-svm-web,94.4.21.11:1194,Sat Jun  8 10:01:02 2019
192.168.0.0/24,tst-svm-web,94.4.21.11:1194,Sat Jun  8 09:57:54 2019
10.8.0.10,note-tst,192.168.1.1:35510,Sat Jun  8 10:01:21 2019
GLOBAL STATS
...