znc: 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/znc - from package: znc

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

On Debian possible default full paths are:

/usr/bin/znc - from package: znc

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

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