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

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

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