weather in the openweathermap?

Your code is much more readable if you put it into a code blocks.

var unit = "metric";

(:background_method)
function initialize() {
    Sys.ServiceDelegate.initialize();
    if (Sys.getDeviceSettings().temperatureUnits == System.UNIT_STATUTE){
        unit = "imperial";
    }
}

(:background_method)
function onTemporalEvent() {
    getWeather();
}

(:background_method)
function getWeather(){
    var lat, lon;

    lat = Application.getApp().getProperty("lat");
    lon = Application.getApp().getProperty("lon");

    Comms.makeWebRequest(">api.openweathermap.org/.../weather", 
    /*
     * URL
     */ 

    {
        "lat" => lat,
        "lon" => lon,
        "appid" => "2225aec78cbbb36c8f92494c9ede2f64",
        "units" => unit // Celcius.
    },
    /*
     * PARAMS 
     */

    {
        :method => Comms.HTTP_REQUEST_METHOD_GET,
        :headers => {"Content-Type" => Communications.REQUEST_CONTENT_TYPE_URL_ENCODED},
        :responseType => Comms.HTTP_RESPONSE_CONTENT_TYPE_JSON
    },
    /*
     * OPTIONS
     */

    method(:onReceiveWeatherdata));
}

(:background_method)
function onReceiveWeatherdata(response, data){
    if(response != 200){
        Sys.println(response);
        Background.exit({"response" => response});
    } else {
        var result = {
            "cod" => data["200"],
            "lat" => data["coord"][0],
        };

        Background.exit({"weatherdata" => result, "response" => response});
    } 
}

I'm not sure what the (:background_method) annotation is, but it isn't something that we document. If you have code that is called from the background process, it must be annotated with (:background).

Additionally, I'm not sure I understand what you doing here..

        var result = {
            "cod" => data["200"],
            "lat" => data["coord"]["50.09"],
            "lon" => data["coord"]["14.42"],
            "dt" => data["1592930217"],
            "temp" => data["main"]["296.04"],
            "humidity" => data["main"]["35"],
            "icon" => data["weather"][0]["icon"]
        };

It looks like you're trying to get the current conditions as documented here. If the request was successful, data will be a dict as shown in their API response. The code above is trying to find a key named "200" in the response... this is simply never going to be found. It looks like you want "cod" => data["cod"]. Similarly, for the lat/lon fields, you want to extract the "lat" and "lon" fields from the "coord" dictionary...

var result = {
    "cod" => data["cod"],
    "lat" => data["coord"]["lat"],
    "lon" => data["coord"]["lon"],
    ...
};

That should get you a pretty good idea of what you need to do.