packetdiag3: command not found

Have You tried accessing the binary with the full path?

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/packetdiag3 - from package: python3-nwdiag

You may install the required package with command apt-get install {package}
Error in other languages:
packetdiag3: bevel nie gevind nie
packetdiag3: comandă negăsită
packetdiag3: comando não encontrado
packetdiag3: commande introuvable
packetdiag3: command not found
packetdiag3: käsku ei ole
packetdiag3: không tìm thấy lệnh
packetdiag3: komanda nerasta
packetdiag3: Kommando nicht gefunden.
packetdiag3: kommandot finns inte
packetdiag3: komut yok
packetdiag3: nie znaleziono polecenia
packetdiag3: níor aimsíodh an t-ordú
packetdiag3: no se encontró la orden
packetdiag3: no s'ha trobat l'ordre
packetdiag3: opdracht niet gevonden
packetdiag3: parancs nem található
packetdiag3: perintah tidak ditemukan
packetdiag3: príkaz nenájdený
packetdiag3: příkaz nenalezen
packetdiag3: команда не найдена
packetdiag3: командата не е открита
packetdiag3: 命令找不到
packetdiag3: コマンドが見つかりません