Remember that you will need to connect to running docker container. So you probably want to use tcp instead of unix socket. Check output of docker ps command and look for running mysql containers. If you find one then use mysql command like this: mysql -h 127.0.0.1 -P <mysql_port> (you will find port in docker ps output).
If you can't find any running mysql container in docker ps output then try docker images to find mysql image name and try something like this to run it:
docker run -d -p 3306:3306 tutum/mysql where "tutum/mysql" is image name found in docker images.