There are actually two ways to do it. One is for doing it on a single scene and one for doing it on a bunch of scenes.
You can add Pins 
. In the Pin Manager 
you can configure the displayed data 
and then you can export 
it to text file.
Pins are also explained in this short Video Turorial.
You can find more tutorials like this on our tutorials page:
If you want to do it on several scenes for a multiple locations you can use the PixEx tool.
You can find it at Raster / Export / Extract Pixel Values
This tool can also be used from the command line.
For more information on this tool, please have a look at the help pages.
