CMB select with data from CPT

Use a function that returns an array of arrays that the options field expects.

Something like this (untested code):

array(
    'name' => 'Test Select',
    'desc' => 'field description (optional)',
    'id' => $prefix . 'test_select',
    'type' => 'select',
    'options' => get_myposttype_options('myposttype'),
),

function get_myposttype_options($argument) {

    $get_post_args = array(
        'post_type' => $argument,
    );

    $options = array();
    foreach ( get_posts( $get_post_args ) as $post ) {
        $title = get_the_title( $post->ID );

        $options[] = array(
            'name'  => $title,
            'value' => $title,
        );
    }

    return $options;
}