Issue the following command:
sudo netstat -na|grep tcp
…which should show something like:
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN tcp 0 0 192.168.0.11:22 192.168.0.184:39662 ESTABLISHED tcp6 0 0 :::22 :::* LISTEN
NOTE: The 0.0.0.0 in the first line indicates that SSH is listing on all ports.
The 2nd line can be ignored. This is simply the current connection.
Similarly, the ::: in the 3rd line indicates that SSH is listing on all ports with IPV6.