qml: 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/qml - from package: qt5-qtdeclarative-devel
/usr/lib64/qt5/bin/qml - from package: qt5-qtdeclarative-devel
/usr/lib/qt5/bin/qml - from package: qt5-qtdeclarative-devel

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

On Debian possible default full paths are:

/usr/bin/qml - from package: qtchooser
/usr/lib/x86_64-linux-gnu/qt5/bin/qml - from package: qml

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

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