How can I recover a standard user's password using the admin password?
Nope is the general prognosis for this.

Assign them a new password if you don’t intend to crack / reverse engineer the password or hope to find it stored in a plan text file.


https://github.com/octomagon/davegrohl


If you just need to get at the files and not crack to get at the user keychain, use the system preferences and an admin account to make a new password for the user account in question.