gnunet-gns: 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/gnunet-gns - from package: gnunet

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

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