You need to find the device path of your CD drive.:

drutil status

Look through the status info for the CD dvice path. It will look like /dev/disk3 or /dev/disk1 depending on your hardware. You then need to unmount the disk:

diskutil unmountDisk /dev/disk3

Now you can use use dd to make an image:

dd if=/dev/disk3s0 of=file_name.iso

To mount the image you created:

hdiutil mount file_name.iso