checkbox-cli: 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/checkbox-cli - from package: checkbox-ng

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

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