something like this:

source = FindObject($alarm.sourceObject());

j = JsonObject();
j.set("id", $alarm.id);
j.set("state", $alarm.state);
j.set("severity", $alarm.severity);
j.set("message", $alarm.message);
j.set("source", source ? source.name : "");
j.set("eventCode", $alarm.eventCode);
j.set("eventName", $alarm.eventName);

trace(0, j.serialize());

I highly recommend you to read https://www.netxms.org/documentation/nxsl-latest/.

What I'd do:

• create Action which runs external shell script to form  json and send query using curl. Pass required event fields as arguments to the script.
• add this Action to EPP (I'd create separate rule just for this integration - this way you can control what exactly being sent)

Or, you setup web service (Settings -> Web service definition), and call it from NXSL. But again, I'd use action for that, not hook.

Note on the json string escaping: instead of manual processing, you can use construct https://netxms.org/documentation/nxsl-latest/#class-jsonobject and produce perfectly valid json.

function main()
{
  webhook = "https://my.host.hstgr.cloud/webhook-test/netxms-alarm";

  payload = "{"
      + "\"id\":\""        + ToString($alarm->id) + "\","
      + "\"state\":\""    + ToString($alarm->state) + "\","
      + "\"severity\":\""  + ToString($alarm->severity) + "\","
      + "\"message\":\""  + EscapeString(($alarm->message != null) ? $alarm->message : "") + "\","
      + "\"source\":\""    + (($alarm->sourceObject != null) ? EscapeString($alarm->sourceObject->name) : "") + "\","
      + "\"eventCode\":\"" + ToString($alarm->eventCode) + "\","
      + "\"eventName\":\"" + EscapeString(($alarm->eventName != null) ? $alarm->eventName : "") + "\""
      + "}";

  WriteLog(0, "Alarm JSON: " + payload);

  cmd = "curl -s -X POST -H 'Content-Type: application/json' -d '" + payload + "' " + webhook;
  Execute(cmd);
}

function EscapeString(s)
{
  if (s == null)
      return "";
  s = Replace(s, "\\", "\\\\"); 
  s = Replace(s, "\"", "\\\""); 
  return s;
}

Webhook | Nodes | n8n Docs

Learn how to use the Webhook node in n8n. Follow technical documentation to integrate Webhook node into your workflows.

(docs.n8n.io)

Thanks.