'On Linux (Ubuntu) I do the same thing: we go to "System", then to "Preferences" and then "Network Connections". We go to the "Wireless" tab and click on the "Modify" button. Then go to the "Security" tab and click in the box next to "Password display".'

Another way is to right click on the Wi-Fi symbol, select "Edit Connections", select the connection, Select "Connection" then "Wi-Fi Security" and "Show Password".