Smoothieboard v1 currently does not have a native Wifi interface.

However, it is possible to easily make it Wifi-capable by connecting it's Ethernet interface to a simple Wifi/Ethernet bridge.

For example, this $15 Wifi/Ethernet bridge will easily make your Smoothieboard Wifi-compatible.

For instructions, see the manual of the bridge you select.

This also generally has the advantage of being much more reliable and efficient than an “on-board” Wifi system which can be found on a few other CNC controller boards.