Currently the platform does not automatically display the height of a stockpile when it calculates the volume. Luckily, it is very easy to do this manually using the Elevation spot height tool.
This allows you to click on the top of the stockpile and it will return it's height.
If you are dealing with a site that has data captured across multiple dates, you'll also see a chart on the left showing how that exact point has changed across data sets.
For stockpiles where it isn't so obvious where the top of the stockpile is, you can use the Elevation overlay to make it easier to locate the highest point - this can be found in the left menu under 'Overlays'.