what-patch: 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/what-patch - from package: devscripts

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

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