Create a subdomain pointing to other sobdomain (in a external server)

Point observatorio.funides.com to your droplet and add the server block below to your NGINX configuration.

server {

  listen 80;
  listen 443;

  server_name observatorio.funides.com;

  location / {
    return 301 https://funides.kingdatasolutions.com$request_uri;
  }

}

Adjust this part of the entry return 301 https://f... to reflect if the destination is using SSL or not.

You could add a CNAME entry to observatorio.* that points to funides.kingdatasolutions.com

On the destination server (funides.kingdatasolutions.com) you will need to add an entry for observatorio.funides.com to handle it properly.