xwininfo: 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/xwininfo - from package: xorg-x11-utils

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

On Debian possible default full paths are:

/usr/bin/xwininfo - from package: x11-utils

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

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