# root required
# Currently Android Stores WiFi Credentials here:
cat /data/misc/apexdata/com.android.wifi/WifiConfigStore.xml

# Although it was in different locations in older versions of Android
# one way to quickly search would be to grep for a known SSID you have stored
# most likely in /data/misc and ignore Binary files
# in this case I'm searching for xfinity SSID
grep -r xfinity /data/misc/*|grep -v Binary

# you can easy copy this file to another devices
# but note that you might need to manually changed some
# stored MAC Addresses or the two devices might fight for a position 
# on a network,which will cause them to randomly kick each other off
# the network