I'm going to suppose that you have the ssh client and server running in the machines , so your problem is not there.
Because you don't give so much information, I'm also going to suppose that your problem is a network configuration problem (as daniel-marchall suggested in his comment) and not a software problem:
Usually, the wifi routers work with two different networks, one is the network with your public ip, and the other is a network with private ips, where all your devices are connected (it depends on your company, but usually these ips are something like 192.168.x.y, or 10.0.x.y)
When your computer wants to connect to an external site (i.e., to an ip that not belongs to your private network), your router 'transfers' your packets from the private network to the public network, but changing the packets slightly (basically, it changes your private ip with its public ip). Doing that, allows an external site to sent the packets back to your router.
When your router receives a packet through its public interface, it determines where it should go this packet based in some internal data and metrics (look for NAT if you want for info), and it transfers the packet from the public interface to your private network (again, changing some details of the packet like the destination ip).
What you want to do is to connect to the public interface of the router (through ssh to the public ip), and then, the router should transfer the packets to your machine. The problem is that in this case, you need to help the router with the transfer, because it hasn't enough information about what to do with the ssh package.
For doing that, the easiest way is with port forwarding (again, as daniel-marchall before). That means that you should enter into the configuration of your router, and configure it saying "hey, all packets that arrives to your public interface at port number 22, you should transfer them to my private ip".
The configuration process depends on the model of your router. Look for it on google, because there are tons of manuals over there.
Other problems that you can have is that you cannot modify the router configuration (and maybe with an inverse tunnel you could do it), or thousand of other different problems, but we need more information for helping you.