How is a Seed stored in an IOTA wallet? Can I gain my Seed back if I lose it?
The seed is stored in your Stronghold backup encrypted by your Stronghold password.
When you have a stronghold backup and your stronghold password, you can import the backup into a new stronghold database and look at the record with record path
iota-wallet-seed to retrieve your seed. As far as I know, the official wallet clients (Firefly and the CLI wallet) do not provide any means for it, though.
Despite the security tag, this is not a security issue: When you have the Stronghold backup and password, you can also import it into Firefly and move all funds wherever you like. Therefore make sure that nobody gets access to both of them at once.