gparted-pkexec: 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/gparted-pkexec - from package: gparted

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

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