Question: If a wireless network does not assign an ip address/gateway ( automatic connection settings) automatically after connection,

how can I find/setup correct ip and gateway address after connecting to the network?

Answer: 
You could try listening on the wifi interface with [wireshark](http://www.wireshark.org/download.html). If anything else on the network knows the gateway, you'll see ARP requests for it. You'll at least get an idea of the network range from the traffic you see.
Sounds like DHCP is disabled.

The default IP address of most routers is 192.168.0.1, check your documentation for your router if this is not the case. Different manufacturors certainly use different defaults.

Also if the network has been setup it's very likely whoever administrates it will have changed it from default.