I have added a metabox and inside it i added a secondary title and a text editor but if i write anything it does not save it or show it on my page

You have used $post instead of $_POST in save function. That is why data is not saved.

You have should use :

$_POST[ 'custom_meta2_nonce' ]
$_POST['sec_title']
$_POST['principle_duties']

instead of

$POST[ 'custom_meta2_nonce' ]
$POST['sec_title']
$POST['principle_duties']

Use below code to save data :

function custom_meta2_save($post_id){
    //checks save status
    $is_autosave = wp_is_post_autosave( $post_id);
    $is_revision = wp_is_post_revision( $post_id);
    $is_valid_nonce = ( isset( $_POST[ 'custom_meta2_nonce' ] ) && wp_verify_nonce( $_POST['custom_meta2_nonce' ],basename( __FILE__)) ) ? 'true': 'false';
    if ( ! current_user_can( 'edit_post', $post_id ) ) {
        return;
    }
    //Exit scripts depending on save status
    if( $is_autosave || $is_revision || !$is_valid_nonce ){
        return;
    }

    if( isset( $_POST['sec_title'] ) ){
        update_post_meta( $post_id , 'sec_title', sanitize_text_field( $_POST[ 'sec_title'] ) );
    }

    if( isset( $_POST['principle_duties'] ) ){
        update_post_meta( $post_id , 'principle_duties', sanitize_text_field( $_POST[ 'principle_duties'] ) );
    }
}
add_action('save_post', 'custom_meta2_save');

you can use custom page template file or page template file To display data in page:

$sec_title = get_post_meta( get_the_id(), 'sec_title', true );
$principle_duties = get_post_meta(get_the_id(), 'principle_duties', true);

echo "Secondary ID :".$sec_title;
echo "<br>Principle duties :".$principle_duties;

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