stg-k: 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/stg-k - from package: stgit-contrib

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