pk-example-frobnicate: 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/pk-example-frobnicate - from package: polkit-devel

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

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