qbittorrent-nox: 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/qbittorrent-nox - from package: qbittorrent-nox

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

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