Getting featured image setting as background

There are some mistakes in the code you are using (AFAIK):

1. get_post_thumbnail_id($post->ID, 'ttrust_post_thumb_big') only has one parameter, that is post_id. So, it should just be get_post_thumbnail_id($post->ID)

2. '' — there’s no 4th parameter for wp_get_attachment_image_src

3. array( 5600,1000 ) defines the $size of the image you want to be shown. You should be using 'large' (string) since that’s what you said you need.

Okay, now try this:

<a href="https://wordpress.stackexchange.com/questions/58960/<?php the_permalink() ?>" rel="bookmark" class="imagewrap">
    <div style="background: url(<?php wp_get_attachment_image_src( get_post_thumbnail_id(), 'large' ); ?>) !important;"></div>
</a>

Reference links: get_post_thumbnail_id, wp_get_attachment_image_src