It looks like you want to get the value from ACF? If so, you can use get_field:
$thumb_title = get_field( 'thumb_title', get_the_ID();
But wait: that won’t work because of this:
'id' => "{$prefix}thumb_title",
The {$prefix} part is defined somewhere in that file, and it’s creating a full field name. You’ll need to include that in your calls to get_field:
// In your file adding fields somewhere:
$prefux = 'myprefix_';
// In your template:
$thumb_title = get_field( 'myprefix_thumb_title', get_the_ID() );
It might be helpful to show us the line where $prefix gets defined in your first block. Also, if these are just regular WordPress meta fields, you would just need to do something like this instead:
$thumb_title = get_post_meta( get_the_ID(), 'myprefix_thumb_title', true );