knetwalk: 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 CentOS possible default full paths are:

/usr/bin/knetwalk - from package: kdegames

You may install the required package with command yum install {package}

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