How to add % on a graph

Here's are a few examples of how to do what you require.  I believe the first link is exactly what you are looking for while the second link is a more complex data visualization variation:

https://www.techrepublic.com/blog/microsoft-office/displaying-percentages-as-a-series-in-an-excel-chart/

http://leapica.com/blog-stacked-bar-chart/