Your laptop cannot auto-discover devices behind a NAT. If it could, anyone on the internet could get into your network, too. If you are using port forwards, I'd suggest locking them down to only your NetXMS server.
Alternatively you can look at Agent Tunnels. In those setups, the Agent will establish a connection to the server as opposed to the server connecting to the client.
The server obviously must be reachable from the client. If both are behind a NAT you'll need to open a port somewhere. Opening the server side up means you only have to do it once to the server, not for every single agent behind a NAT. If you can lock that down for some additional security depends on your setup.

There have been a lot of posts regarding Agent Tunnel setups over time, I recommend searching the forum (and for additional questions to create a post in the support, as opposed to the development one).