mk-job: 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 CentOS possible default full paths are:

/usr/bin/mk-job - from package: check-mk-agent

You may install the required package with command yum install {package}

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