Assuming that you are using a Windows 8, 8.1 or 10 PC connected to the WiFi that you want to find the password for…
Right click on the Wireless icon in the system tray (bottom right hand side of the task bar)
Left click on “Open Network and Sharing Centre”
Under the section “View your active network”, left click on the blue words “Wireless Network Connection”.
Left click on the “Wireless Properties” button
Left click on the “Security” tab
Left click on the “Show characters” box.