Android - How can I find a saved Wi-Fi password?

On my phone, the credentials are stored in /data/wifi/bcm_supp.conf. You'll probably need root to see it directly on your phone but you may be able to use adb pull (requires the Android SDK) from your PC to get the file.

As noted in the comments, the location may vary based on your ROM or device (specifically the Wi-Fi chip; mine's a Broadcom). Check /data/wifi/, /data/etc/wifi/ and /data/misc/wifi/ for relevant config files if you don't find the ones suggested by eldarerathis or me.

On CyanogenMod devices, and possibly other AOSP ROMs, you should be able to grab it from the /data/misc/wifi/wpa_supplicant.conf file. On a non-rooted device I don't think this is possible since you won't have permission to read the /data directories where the settings are stored and the Settings menu simply displays (Unchanged) if you go into the network configuration.

This is what I see on my CM7 EVO (network name and password redacted):

# cd /data/misc/wifi/
# ls
sockets              wpa_supplicant.conf
# more wpa_supplicant.conf
ctrl_interface=eth0
update_config=1

network={
        ssid="SomeWifiNetwork"
        psk="MyPlaintextPassword"
        key_mgmt=WPA-PSK
        priority=1
}
#

In Android Oreo and Pie (tested on OnePlus 6), the file seems to be /data/misc/wifi/WifiConfigStore.xml which stores your Wi-Fi credentials. I do not know of a good XML parser, but the file can be opened in a text editor (requires root access). Search with the name of your Wifi (SSID) and locate the line containing:

<string name="SSID">&quot;YOUR_SAVED_SSID;</string>

One of the following lines would show the password. It would be mentioned as "PreSharedKey". Example:

<string name="PreSharedKey">&quot;SAVED_PASSWORD;</string>