I'm not good with networking and maybe I'm using a wrong wording but I cannot find an answer. I'm using Ubuntu Desktop and I'd like to receive my ssh traffic via one of my connections and all ther rest of my traffic via some other connection. How can I achieve this?
Please read sshd_config what formats of ListenAddress are supported.
You should specify the IP of your Ethernet card, I assume it is fixed (otherwise you'll have a lot of hoops to jump through).
To isolate traffic from the WiFi I would suggest to use a firewall (e.g.
ufw) and disable incoming connections on port 22.