dnsspoof: 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 CentOS possible default full paths are:

/usr/sbin/dnsspoof - from package: dsniff

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/dnsspoof - from package: dsniff

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

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