gnunet-transport-certificate-creation: 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-transport-certificate-creation - from package: gnunet

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

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