knotes: 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/knotes - from package: kdepim

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

On Debian possible default full paths are:

/usr/bin/knotes - from package: knotes

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

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