This GET endpoint is used to retrieve a single wallet by its wallet_token: your own client wallet (clnt_wlt_ token, type CLIENT_FUNDS) or a wallet of one of your users (usr_wlt_ / mp_card_ token, type USER_FUNDS / MASSPAY_CARD).
The response is the same wallet object GET /wallet/USER_TOKEN lists: type tells whether it is a client or a user wallet, user_token is present for user wallets only, balance and currency_code give the current balance, client_paying_fees / fee_wallet_token describe who pays the wallet's fees, card_type / last_4 are returned for card wallets and wiring_instructions when deposit instructions are available for the wallet.
A wallet that does not exist or does not belong to your account answers 404.