As of today's version of Google Sheets (on Dec 6, 2019), we can do this to make the values appear:
Create your pie chart (assuming you know how)
Click in the upper right of the chart, on the 3 dots. "Chart editor" will appear on the right.
Under "Chart editor", there will be "Setup" and "Customize". Click on "Customize"
There should be a selection for "...
You are analysing data for 'line of best fit' where there are missing elements in the data range. How to interpolate data in a range in Google Sheets has provided a custom function with which to identify the missing elements.
The following formula attempts to provide a method by which the interpolated data can be calculated.
The formula is a combination of ...