If you do not have a phone with GPS or use a tablet with Wi-Fi that does not have GPS, it is still possible to play Pokemon Go. Unfortunately, the experience will not be as good as you need to be in areas that have strong Wi-Fi signals, such as restaurants, bars, coffee shops or other businesses where you can connect.
Since GO Pokémon is based on having an Internet connection, you will be able to locate your device with only a Wi-Fi signal, just do not expect to compete on the same level as your friends with Android phones.