how can I query all wordpress users of a blog

Refer to the get_users() Codex entry.

$users = get_users();

You can pass the function an array of arguments, including:

$args = array(
    // Order by username (display name)
    // Note: 'login' is default
    'orderby' => 'display_name',
    // Order (note: 'ASC' is default)
    'order' => 'ASC'
);

$users = get_users( $args );