Bonobo command line interface contains a graphviz code generator that can be used to visualize any graph you wrote (this is available since 0.5).
I will assume you already wrote a transformation graph in a file called transform.py, that is valid (you can run it, using bonobo run).
Graphviz use a graph description language called “dot”, that it can use to generate various image formats. If you do not have graphviz installed, download and install it now.
Now, let's use bonobo inspect to generate a graph source file.
$ bonobo inspect --graph transform.py > transform.dot
You should not see any output, but you now have a transform.dot graphviz source file that you can use to generate pictures of your graph.
$ dot -o transform.png -T png transform.dot
You now have a transform.png file to understand what you're working with, or eventually document your transformations.
You can also do it using a one liner.
$ bonobo inspect --graph transform.py | dot -o transform.png -T png