xfconf-query: 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/xfconf-query - from package: xfconf

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

On Debian possible default full paths are:

/usr/bin/xfconf-query - from package: xfconf

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

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