This guide would come in handy if only you've successfully connected to the Wi-Fi previously but have forgotten the password.
- I shall not the held responsible for whatever you decide to do with this info
- This hasn't been tested on Marshmallow (but you can still try it)
- wifiKeyRecovery.apk (download from the attachment below)
How to View or Retrieve Forgotten Wi-Fi Passwords on Android Devices
- Install the apk and launch it
- Once the application opens, you'll see a list of all previous connected Wi-Fi devices (SSIDs and Passwords)