echo get_the_author_meta () | WordPress.org

The entire source code in which this is executed would be helpful. Probably the 2nd parameter is set incorrectly. But at the moment we can only guess.

XXXXXXXXX is where I need to print:

add_action( 'show_user_profile', 'my_show_extra_profile_fields' );
add_action( 'edit_user_profile', 'my_show_extra_profile_fields' );
add_action( "user_new_form",'my_show_extra_profile_fields' );
function my_show_extra_profile_fields( $user ) { ?>

.....

.......

<table>
<h1 id="prezzo_settimana">Listino prezzi</h1>XXXXXXXX</table><br></br>


<table>

show_user_profile specifies the WP_User object as the 1st parameter. Actually, everything you are looking for is already contained there.

Example:

echo $user->display_name;