STKDemo: 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/STKDemo - from package: stk

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

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