How do I, in Ubuntu, determine what the formatting (e.g FAT etc.) of an SD card is?
Use the fdisk /dev/whicheveryourdevice is.
You can determine which device your SD card is by running dmesg.
If it's mounted, you can try using the mount command to see what the format is.
If not, you can try running gparted (or disk utility if that's in your menus) to have it tell you the partition's format.
Just be careful not to change the partitions, only view the information. Gparted makes it quite explicit (you have to "apply" potential changes in order for anything to happen).