If you started cntlm as a system service on startup you can call sudo service cntlm status
to see the current status and view the last ten connection messages, that should look something like this:
sschneid@sschneidschnee ~ $ sudo service cntlm status
● cntlm.service - LSB: Authenticating HTTP accelerator for NTLM secured proxies
Loaded: loaded (/etc/init.d/cntlm; bad; vendor preset: enabled)
Active: active (running) since Mi 2018-04-04 08:29:25 CEST; 2h 7min ago
Docs: man:systemd-sysv-generator(8)
Process: 1483 ExecStart=/etc/init.d/cntlm start (code=exited, status=0/SUCCESS)
Tasks: 11
Memory: 3.1M
CPU: 1.670s
CGroup: /system.slice/cntlm.service
└─1620 /usr/sbin/cntlm -U cntlm -P /var/run/cntlm/cntlm.pid
Apr 04 10:35:06 M0024 cntlm[1620]: 127.0.0.1 CONNECT media-cdn.ubuntu-de.org:443
Apr 04 10:35:06 M0024 cntlm[1620]: 127.0.0.1 CONNECT media-cdn.ubuntu-de.org:443
Apr 04 10:35:06 M0024 cntlm[1620]: 127.0.0.1 CONNECT media-cdn.ubuntu-de.org:443
Apr 04 10:36:18 M0024 cntlm[1620]: 127.0.0.1 CONNECT krebsonsecurity.com:443
Apr 04 10:36:19 M0024 cntlm[1620]: 127.0.0.1 CONNECT www.youtube.com:443
Apr 04 10:36:20 M0024 cntlm[1620]: 127.0.0.1 CONNECT www.google.com:443
Apr 04 10:36:21 M0024 cntlm[1620]: 127.0.0.1 CONNECT i.ytimg.com:443
Apr 04 10:36:21 M0024 cntlm[1620]: 127.0.0.1 POST http://ocsp.pki.goog/GTSGIAG3
Apr 04 10:36:33 M0024 cntlm[1620]: 127.0.0.1 CONNECT tiles.services.mozilla.com:443
Apr 04 10:36:34 M0024 cntlm[1620]: 127.0.0.1 CONNECT img-getpocket.cdn.mozilla.net:443
Generally, CNTLM logs to SYSLOG, so that would be another spot to search for your logged information.