On , I learnt ...

How to list the mounts of a running Docker container

Use docker inspect like so:

$ docker inspect -f "{{ .Mounts }}" $CONTAINER_ID

I used this to determine where a Discourse Docker container was persisting its logs:

$ docker inspect -f "{{ .Mounts }}" $(docker ps -q --filter="name=app")
[{bind  /var/discourse/shared/standalone /shared   true rprivate} {bind  /var/discourse/shared/standalone/log/var-log /var/log   true rprivate}]

Here you can see logs are mounted from /var/discourse/shared/standalone/log/var-log.