mkdtskel: command not found

Have You tried accessing the binary with the full path?

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/mkdtskel - from package: libxml-dt-perl

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