A while ago I made a tutorial on Getting WiFi Passwords With Python which provides a script that automates the following process. For those that don't want to install Python, this is how to identify stored WiFi passwords manually.

Identifying the Target Profile

First, you need to identify the profile associated with the stored WiFi connection. To do this, open the command prompt and execute the following.

netsh wlan show profiles

You should get an output that looks something like this:

User profiles
    All User Profile     : WiFi Network 1
    All User Profile     : WiFi Network 2
    All User Profile     : WiFi Network 3
    All User Profile     : WiFi Network 4
    All User Profile     : WiFi Network 5
    All User Profile     : Other WiFi Network 6
    All User Profile     : Yet another WiFi Network 7

This output shows the associated profile for each of your stored WiFi connections. Copy or remember the exact text of the profile, e.g. WiFi Network 2 as it will be used in the next step.

If your WiFi SSID/name is not in this list, you will not be able to identify the password as it is not a stored connection.

Obtaining the Profile's Password

In cmd again, execute the following after replacing the profile name:

netsh wlan show profile "<profile name>" key=clear

For me, I would execute netsh wlan show profile "WiFi Network 2" key=clear as I am looking for the password associated with the profile WiFi Network 2.

This will output some information about the network, if you go down to Security settings and look beside Key Content, you will see your WiFi password.

Security settings
    Authentication         : WPA2-Personal
    Cipher                 : CCMP
    Authentication         : WPA2-Personal
    Cipher                 : GCMP
    Security key           : Present
    Key Content            : yourpassword!   <-- here is the WiFi password