Answer by mwfearnley for UUID Of A drive that won't show up in /dev/disk/by-uuid or blkid

I have found that file -s can give the UUID for a partition in a case where blkid will not:

sudo file -s /dev/sda1/dev/sda1: Linux rev 1.0 ext2 filesystem data (mounted or unclean), UUID=ef55765f-dae5-426f-82c4-0d98265c5f21 (needs journal recovery)

If it detects something else (e.g. DOS/MBR boot sector), try adding -k to return all matches.