Is it possible to connect an external CD/DVD drive to an iOS device?
No. There is no way to interface a CD drive with an iOS device. The best way to do this is to have your iOS device registered to a copy of iTunes running on a Mac or PC, and to connect the iOS device to the Mac or PC via WiFi or a USB cable. This would presuppose that you have a suitable CD drive connected to the Mac or PC for ripping audio.

However, it occurs to me that you could probably rip music to AAC or MP3 format on a Mac or PC and then email those files to yourself, check the email on your iOS device, and then open the email attachments on the iOS device. That would get the music files in there.