How can I find what /dev my DVD-drive is?

Put a disk into the drive, wait until OS X mounts it, and then type the following command in the Terminal:

$ mount
[⋮]
/dev/disk2 on /Volumes/MyDisk (cd9660, local, nodev, nosuid, read-only, noowners)

In my case, the drive is located at /dev/disk2.

You can use drutil as well.

# drutil status
 Vendor   Product           Rev 
 MATSHITA DVD-R   UJ-857D   KBVB

           Type: DVD+RW               Name: /dev/disk2
[⋮]

Finally found a way. Not sure if it is the best, but it works anyways:

df -h

c",)

Start Utilites, Disk Util. Click the drive or partition on the left, then the blue i/info icon in the toolbar. The disk identifier is the name to be used after /dev/