gwakeonlan: 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/gwakeonlan - from package: gwakeonlan

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

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