dnstcpbench: 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/bin/dnstcpbench - from package: pdns-tools

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

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