please check your postype and add arg
<?php
$query = new WP_Query( array( 'post_type' => 'ourproducts' ) );
if ( $query->have_posts() ) :
while ( $query->have_posts() ) :
$query->the_post();
?>
<h3><?php echo get_field('nasi_proizvodi'); ?></h3>
<?php
endwhile;
wp_reset_postdata();
endif;
?>