Creating an article via Web Services allows you to populate fields:-

{{base_path}}/api/index.php/v1/content/articles

$data = [

'title'       => $title,
'articletext' => $message,
'catid'       => $categoryId,
'language'    => '*',
'metadesc'    => '',
'metakey'     => '',

'metadata' => 
[
'robots' => '',
'author' => '',
'rights' => '',
],

'images' =>
[
'image_intro' => 'images/site/fb/'.$filename.'jpg',
'image_intro_alt' => $filename,
'image_intro_caption' =>'',

'image_fulltext' => 'images/site/fb/'.$filename.'jpg',
'image_fulltext_alt' => $filename,
'float_fulltext' => '',
'image_fulltext_caption' => '',
],

'state' => '1',
'created_by' => '111',
'created_by_alias' => 'Test User',
'created' => $created,

];

There doesn't appear to be a way of populating the Schema.

And no Schema data is provided in a GET request {{base_path}}/api/index.php/v1/content/article/{{article_id}}