Confused me too. From what I gather
, it looks like a Unix command, so it is something you don't do in K3b.
So open up a terminal/console/shell (konsole) window and type
dd bs=1k if=image.nrg of=image.iso skip=300
(You'll probably have to change directories to the location of the .nrg file)
Replace image.nrg with then name of your .nrg file (something.nrg), replace of with the name you want your outgoing file to be (something.iso)
Then burn the disc using K3b and the .iso file that you just created.