You need to add some category to all your Blog posts? You can set your Posts’ categories under each post – under Categories in the right. What do you mean by “but I can’t seem to call the category for each post” … I think I am missing something here…

I tried get_category() and a number of other category related php calls but can’t figure it out.

https://codex.wordpress.org/Function_Reference/wp_get_post_categories

In the file includes/shortcodes/vc/boc_post_grid.php I added the following just beneath line 38: $excerpt = get_the_excerpt(); …

$categories = get_the_category();
$separator = ' ';
$output_cats = '';
if($categories){
foreach($categories as $category) {
$output_cats .= '<a href="'.get_category_link( $category->term_id ).'" title="' . esc_attr( sprintf( __( "View all posts in %s" ), $category->name ) ) . '">'.$category->cat_name.'</a>'.$separator;
}
}

Then in line 74, I added the div feat-pic-category and contained code after the featured image and overlay code so it looks like this…

$str .='<div class="pic '.esc_attr($img_hover_effect).'"><a href="'. get_permalink().'"><img src="'.esc_url($feat_img).'"/><div class="img_overlay"><span class="hover_icon icon_plus"></span></div></a></div><div class="feat-pic-category"><span>'.trim($output_cats, $separator).'</span></div>';

Then I styled accordingly.

Thanks for sharing this, may I see what the outcome looks like? Cheers!