mitmdump: 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/mitmdump - from package: mitmproxy

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

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