Connect to laptop (behind NAT) using intermediary server
We'll use a combination of ssh remote and local port forwarding in order to expose the laptop's ssh port outside the NAT. The laptop must initiate the forwarding.
On the server
Make sure you have an account that the laptop can connect to through ssh.
On the laptop
This will initiate a connection to the server (from the laptop), and it will set-up a remote port forward such that dialing localhost:12345 on the server will forward to localhost:22 on the laptop.
ssh -N -R 12345:localhost:22 email@example.com
On the other client
This will connect to the server, and then set-up a local port forward (from the other client to the server) such that dialing localhost:12345 on the client will connect to localhost:12345 on the server. Of course, localhost:12345 on the server just forwards to localhost:22 on the laptop.
ssh -N -L 12345:localhost:12345 freedom.mgk.ro
Then from another terminal (still on the other client) you can
ssh -p 12345 ubuntu@localhost
And should reach localhost:22 on the laptop.