如何在wordpress的管理面板中复制类别子菜单

How to create a second category menu like Seminars >> seminars >> create new seminars >> seminar categories and then I want to duplicate seminar categories and make it Seminar venues with inside remaining the same.

See attached screenshot:

As per my understanding, you just want to create a new taxonomy under Seminars. If you make changes in theme files you can edit the function.php and add the following code

$labels = array(
        'name'              => _x( 'Seminar Venue', 'taxonomy general name', 'textdomain' ),
        'singular_name'     => _x( 'Venue', 'taxonomy singular name', 'textdomain' ),
        'search_items'      => __( 'Venue', 'textdomain' ),
        'all_items'         => __( 'All Venues', 'textdomain' ),
        'parent_item'       => __( 'Parent Venue', 'textdomain' ),
        'parent_item_colon' => __( 'Parent Venue:', 'textdomain' ),
        'edit_item'         => __( 'Edit Venue', 'textdomain' ),
        'update_item'       => __( 'Update Venue', 'textdomain' ),
        'add_new_item'      => __( 'Add New Venue', 'textdomain' ),
        'new_item_name'     => __( 'New VenueName', 'textdomain' ),
        'menu_name'         => __( 'Venue', 'textdomain' ),
    );

    $args = array(
        'hierarchical'      => true,
        'labels'            => $labels,
        'show_ui'           => true,
        'show_admin_column' => true,
        'query_var'         => true,
        'rewrite'           => array( 'slug' => 'genre' ),
    );

    register_taxonomy( 'genre', array( 'seminars' ), $args );

Or you can use the plugin Custom Post Type UI. In this plugin go to taxonomy and add a new taxonomy under your post type "seminars"