I didn't click the link to the workshop. The way I would do it is to use the
getTips api call. This will return all tips including old stale one.
However, by examining the IRI code we can see that we have FIFO list that keeps the tips, so I believe that the first one will be the newest transaction...
Note that if the node tries to solidify a path, then the newest transaction the node receives may not necessarily be a tip.