Here is a quick tutorial on adding a customizable point to the end/start of your line chart. We are aiming to produce the below chart.
How to Build
You can add use this to create charts with custom shapes by selecting Shapes rather than Circle. This allows a lot of customization! Try playing around with it. You may not need to do this if you simply need a point to highlight the most recent value at the end of the line.
Check out this blog on dual axes charts written by Robert Headington (DS13):
More info on dual-axis and when its right to use (Katharine Pearce, DS12)