Show post count number assigned to custom taxonomy

Normally usage of get_term() or get_term_by() is pretty much clear cut. See the basic example below:

// ID is needed
$term_by_id = get_term( 12345, 'destination' );
echo $term_by_id->count;
// Or if you e.g. want use the name (or slug or id or term_taxonomy_id)
$term_by_name = get_term_by( 'name', 'greece', 'destination' );
echo $term_by_name->count;

Note: I said normally, because I don’t know anything about the plugin you are using.