Hi Juan I read your post and I was pluzzed in how to plot this on Knime, I read this post "From D3 example to interactive KNIME view in 10 minutes" which uses the same code of this website http://bl.ocks.org/oyyd/859fafc8122977a3afd6.
I managed to load the json data (the energy one) and change the code to import the file. I think the problem is that the sankey code is calling a function called d3.sankey() which is in a library: https://github.com/d3/d3-sankey/releases/tag/v0.7.1. For that reason I was NOT able to plot the Sankey.
Please find attached the workflow if helps.