The attached DXP file shows a simple Sankey example using d3. The DXP file is for Spotfire 6.5 so it will work on Spotfire 7.0 and 7.5/7.6 etc.
Before opening the DXP file you will need to have the JSViz extension installed. This can be downloaded from here:
Here is another example the leverages TERR: https://community.tibco.com/wiki/displaying-sankey-chart-tibco-spotfire-using-tibco-enterprise-runtime-r-and-jsviz
See how to reuse this example: https://community.tibco.com/wiki/how-reuse-spotfire-jsviz-example-and-apply-it-your-data