In jevents you can set a location to en event, but this doesn't attibute a latitude and a longitude to en event even if you can see it on a map. If you see it on a map in jevents, it's because , for shwoing a single location, the location address can bu used and translated.
But when showing multiple locations using the address would take too much time.
This is why locations also have a latitude and longitude fields.
jevents requires a silver memebership to provide a geolocation plugin
www.jevents.net/join-the-club/levels#
This is why we also provide a geocoder plugin using Google and yahoo as a fallback.
Our Geocoder plugin needs to be installed and enabled and will geocode every new events.
FOr older events you need to run our batch geolocator to locate previously added events.
If events do not show on the map , the most obvious reason would be becuse it doen't have latitude and longitude although it has an address set.
You need to check tthe database using your host cpanel phpmyadmin, looking into
#__jevents_vevdetail table (where # is your table prefix)
for the geolat and geolon value for the respective event IDs.