Your questions are unfortunately not very clear....
/dev/null is not a partition---it is a special device which can be thought of as "write only". Anything sent there is never seen again.
Which information contain this partition in Linux ?
I don't know what you mean here...
Things like /dev/sda are not partitions, they are devices. In /dev you will find both character and block devices--If you do ls -l in /dev, you will see the difference in the first letter.
A USB device would not typically show up as /dev/sda1, etc.
The dd command is the low-level equivalent of ghost.