How do I retrieve schema passwords from older version
which, what, where, when, why?
There is no way to get the plain text password out of the database. The best you can do is get the encrypted password for the sake of recreating it.
To do that, go to the schema browser, change object type to USERS, find the user you want, go to the script tab on the right.
It should be there in the “identified by values” clause. If it’s not there, click the first toolbar button on the script tab, then in the dialog that appears, go to the “Users” tab and check "If possible, include ‘identified by values’ clause in 11g and above.
If it’s still not visible, then you don’t have enough privileges. The encoded passwords are in DBA_USERS and ALL_USERS in 10g and older. in 11g and newer, you have to look in SYS.USER$.