you will find the keychain in the utility folder, select the System keychain in the left menu bar, and select Passwords from the category menu. And then select the password from the menu
The keychain will filter your stored password.
then select the wifi for which you are looking for the password.
Then it will open a new window for the stored password, Click on the 'Show password' checkbox.
You will be asked to authenticate with a username and password.
If you are unsure what your username is, open up the Finder app and look for the home icon in the Favorites sidebar. Your home folder will be called the same as your username.
After proper authentication, you will get to know the wifi password in the previous window.
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