How to properly enqueue jQuery knob on WordPress without conflict?

If you want to just enqueue a script by name then you have to register it first with wp_register_script:

wp_register_script( 'jquery-knob',
                    plugins_url( 'assets/js/jquery.knob.min.js', __FILE__ ),
                    array( 'jquery' ), '1.2.11' );
:
wp_enqueue_script( 'jquery-knob' );

However that’s only really useful when you’re registering a script to be available as a dependency for other scripts, which I don’t think you are here. Instead it’s easier to register and enqueue it in one go, which you should do from a wp_enqueue_scripts hook:

function enqueue_jquery_knob() {
    wp_enqueue_script( 'jquery-knob',
                       plugins_url( 'assets/js/jquery.knob.min.js', __FILE__ ),
                       array( 'jquery' ), '1.2.11' );
}
add_action( 'wp_enqueue_scripts', 'enqueue_jquery_knob', 10, 0 );