Problem:
The user was not able to display a field that accepts multiple instances.

Solution:
The field's slug inside the wpv-for-each shortcode needs to be the actuall slug in the database. Toolset fields are saved on the database prefixed by 'wpcf-'. I fixed the shortcode and it is now working, check this screenshot http://prntscr.com/tr9q2d

[wpv-for-each field="wpcf-shortcode-questionari"]
<div>[qsm quiz='[types field="shortcode-questionari"][/types]']</div>
[/wpv-for-each]

Relevant Documentation:
https://toolset.com/documentation/programmer-reference/views/views-shortcodes/

Problem:

Query the related posts for a given page in a short code. When I pass in get_the_ID() or even a specific Post ID, the array I get back contains all children of all posts.

Solution:

You can follow our document to setup the PHP codes with function toolset_get_related_posts().

Relevant Documentation:

https://toolset.com/documentation/customizing-sites-using-php/post-relationships-api/#toolset_get_related_posts