Not talking about a lost wallet with money, but the wallet used for encryption in the Oracle database and with encrypted backup.
A wallet is used for storing keys used to encrypt/decrypt data to/from the database, as with Transparent Data Encryption. The documentation on Advanced Security says that Oracle searches the parameter ENCRYPTION_WALLET_LOCATION in sqlnet.ora, or if not found it searches for WALLET_LOCATION in the same file. If none of them are given it searches in the default location of the wallet for the database. I found different references to where this default location is, depending on underlying OS and version. After a few rounds of trial and error (always receiving ORA-28368) I gave up and resorted to tracing my process:
select p.spid
from v$session s join v$process p on(s.paddr=p.addr)
where s.sid in (select sid from v$mystat);
Then using strace on the process:
strace -p 42
Among the output from strace something like this can be found:
access("/u01/app/oracle/admin/FOO/wallet/ewallet.p12", F_OK) = -1 ENOENT (No such file or directory)
open("/u01/app/oracle/admin/FOO/wallet/ewallet.p12", O_RDWR|O_CREAT|O_TRUNC, 0666) = -1 ENOENT (No such file or directory)
In this case the directory did not exist. It needs to be created with proper privileges for the OS user running the instance (usually oracle).
On Windows I imagine Process Monitor can be used to track down the location.
Morgans Library has a nice reference on wallets .