dnssec-importkey: 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/sbin/dnssec-importkey - from package: bind9

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

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