ah yes that’s it i need to assign a user to a post other than the author.
so i thought i have a workflow-tab for this kind of post and show all posts related to this user.
also i show a button to create a new post for this user.

how can i make sure the users id gets to the new post since it is not the current-user id?

Did it!

$array = array_merge(
    array(0 => "--- None ---"),
    piklist(            
        get_posts(array(
            'post_type' => 'my-custom-post-type',
            'numberposts' => -1,
            'orderby' => 'title',
            'order' => 'ASC'
        )), array('ID', 'post_title')
    )
);
piklist('field', array(
    'type' => 'select'
    , 'field' => 'current_selection'
    , 'label' => __('Current Selection')
    , 'description' => __('Currently selected Post')
    , 'attributes' => array(
        'class' => 'text'
    )
    , 'choices' => $array
));