Creating a bookable USB drive is the same on Kali as it is on Ubuntu or any other Linux distro. First, you must plug in your USB drive and figure out what drive it is (/dev/sda, /dev/sdb). You could use a program like GParted or you could just use the command fdisk -l. Next make sure that your USB drive is not mounted by using the command umount /dev/sdx where /dev/sdx is your USB drive. After you know this, you can use the dd command to write the image to the drive. The command is dd if=/path/to/file.iso of=/dev/sdx bs=512k. Just be sure that you don't write to a partition of the drive (aka /dev/sdx1). This could result in corruption.