cwnnkill: 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/sbin/cwnnkill - from package: freewnn-cserver

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

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