To access an optical disc via USB follow the [typical procedure for attaching a USB device](/doc/usb-devices/#with-the-command-line-tool), then check with the **Qubes Devices** widget to see what device in the target qube the USB optical drive was attached to.
Typically this would be `sr0`.
For example, if `sys-usb` has device `3-2` attached to the `work` qube's `sr0`, you would mount it with `mount /dev/sr0 /mnt/removable`.
You could also write to a disc with `wodim -v dev=/dev/sr0 -eject /home/user/Qubes.iso`.