First, you don’t “ssh to an external drive”. You are using “ssh” to login to the remote computer with an ID, then to see the attached drives you need to go to the “mount” point. It appears you have logged in, and assuming the ID you used has permissions to see the remote drives, see all the mounted devices under /Volumes.
After logging in, you’ll be in a terminal window. do the following (ignoring the hash and comments after)
cd /Volumes # the mount point
ls -l # will show the drives mounted
cd XX # where XX is the device