jwhois: 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/jwhois - from package: jwhois

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

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