mk-build-deps: 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/mk-build-deps - from package: devscripts

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

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