I have never heard of a smartphone without Wi-Fi capability. It should be under Settings -- Connections/
Depending on phone, carrier and country, network settings may be restricted (that whole censorship thing, you know). If the carrier flashed the phone with firmware eliminating Wi-Fi, there's no way to enable it without rooting and re-flashing it. If that were the case, (a) the phone may not work on the carrier and (b) the authority requiring removal of Wi-Fi will find out via packet-sniffers and come knocking on your door).