gwhy: 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/gwhy - from package: why

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

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