From the Kraken manual, it looks like graphs are automatically generated. Also, it looks like Kraken produces a ton of output. You have to be more specific on what you'd like to see plotted.
EDIT: Looks like there are multiple tools named Kraken. Though this question provides no context, seems like you're looking at http://ccb.jhu.edu/software/kraken/ and not at ftp://ftp.ebi.ac.uk/pub/contrib/enrightlab/kraken/SequenceImp/src/seqimp-13-095/doc/imp.html
Like I mentioned earlier, context plays a crucial role in online scientific forums.