gwhois: 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/gwhois - from package: gwhois

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

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