If you need to copy a saved WiFi network's password onto another device or want to find out what it is for another reason, there is a way to look at all of the saved passwords on your Mac using Keychain Access. Keychain Access is Apple's built-in password manager; there, most of the passwords you save on your Mac are stored and encrypted, accessible only with the computer's administrator password. This includes the passwords for all WiFi networks you have saved. To look at those passwords, follow these steps:

  1. Open Keychain Access (it is located in /Applications/Utilities/Keychain Access, although it is sometimes easier to type it into the Spotlight bar on the top right of the menu bar)

  2. Navigate to the System keychain in Keychain Access, under the "Keychains" list
  3. Under Category, select Passwords
  4. In the resulting list of WiFi networks, double-click the one whose password you want to see
  5. A window should then pop up. On the bottom of that window, there is a "Show Password" checkbox. Click it, and enter your administrator name and password.

Keychain Access will display your Wifi network's password, allowing you to see it and copy onto any device you wish.