To access a list of wireless networks from the Linux command prompt use the iwlist tool. Iwlist will produce a list of all the wireless network in range of your device. 

sudo iwlist wlan0 scan

 While this sound good. it doesn't work. If you are in an area were there are many wifi network you get list that is way too long to read. So you will want to pipe the output of the command to less. Less will let you scroll up and down the list. Alternatively you can also pipe it to more. Where hitting space bar will advance the out of the command one page at a time. 

sudo iwlist wlan0 scan | less
sudo iwlist wlan0 scan | more

Type "q" to exit more

If you are using pi make sure you set the country profile the wifi is supposed to use or the wifi will remain disabled. Setting the wrong country may cause your pi to use the wrong frequencies for your local. To do this use the tool/program/app raspi-config. Open the app go to Localization Options then Change wireless country.

raspi-config can be run by typing:

sudo raspi-config

I also recommend setting network interface names to predictable. This is also done in raspi-config under advanced options. 

you will need to reboot for the changes to take effect.