sslsniff: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/sslsniff - from package: sslsniff

You may install the required package with command apt-get install {package}

Error in other languages:
sslsniff: bevel nie gevind nie
sslsniff: comandă negăsită
sslsniff: comando não encontrado
sslsniff: commande introuvable
sslsniff: command not found
sslsniff: käsku ei ole
sslsniff: không tìm thấy lệnh
sslsniff: komanda nerasta
sslsniff: Kommando nicht gefunden.
sslsniff: kommandot finns inte
sslsniff: komut yok
sslsniff: nie znaleziono polecenia
sslsniff: níor aimsíodh an t-ordú
sslsniff: no se encontró la orden
sslsniff: no s'ha trobat l'ordre
sslsniff: opdracht niet gevonden
sslsniff: parancs nem található
sslsniff: perintah tidak ditemukan
sslsniff: príkaz nenájdený
sslsniff: příkaz nenalezen
sslsniff: команда не найдена
sslsniff: командата не е открита
sslsniff: 命令找不到
sslsniff: コマンドが見つかりません