Custom Taxonomy dont save in a frontend form for post a custom post

I think you have used wrong tax_input parameter value for wp_insert_post() function it should be array like this

array( 'taxonomy_name' => array( 'term', 'term2', 'term3' ) )  

as shown in the following code

$my_post = array(
        'post_title'    => $title,
        'post_content'  => $content,
        'post_status'   => 'publish',
        'post_type' => 'faenas',
        'tax_input'    => array( 'faenas_combenef_category' => array( $location ) )
);