journalctl: 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:

/bin/journalctl - from package: systemd

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