In Local Authentication Type user credentials are stored in "User" GeneXus Access Manager table.
GAM does not store the password of the user, but it stores a hash of it. A hash is an algorithm such that given a string, produces always the same resulting string, and given the resulting string you cannot get the original.
The hash is obtained from a unique key for each user and an algorithm named SHA-512 (Secure Hash Algorithm).
This means that when you retrieve GAM Users from the repository, the password property will always have an empty value.