What you looking for is the MAC address of the Wi-Fi chipset.
Start->Settings->Connections then pick the option for Wi-Fi, or, if not, 'Network Cards'. The problem is that this option depends on the Phone manufacturer, and OS version, you may have to dig around to find it. The screen you are after looks like the attached Network1 image. Click on the entry for the Wi-Fi chipset for your device. A screen similar to Network2 will appear.
The MAC address of the card appears in the textbox as a sixteen character hex address. Note that in this particular case the textbox display pairs them up and then drops any leading zeros from the value. It is this address you will have to register with your Wi-Fi router and you may also have to select the Use Specific IP address radio button too, it will depend on how your router is set up.
Trial and error may also be the order of the day.
Your router may also expect the address to entered as separate hex byte values, in this case it would be FE:80:02:1A:6B:FF:0F:E9
Good luck!