FYI you might be interested in this thread with an in-form solution for converting a 'fence' (geoshape or geotrace) to KML.
how could you calculate the distance of those 2 points
If you have two geopoints, eg in a geotrace, you can use the build-in ODK function distance() to get their distance. These dont actually have to come from a geotrace question per se; eg if you have two separate geopoint questions you can still do it; see this thread for description.