When you say “who have added the post”, are you meaning all users who have written at least 1 post of the event post type? If so, you can get all the authors of all events like so:
$event_posts = get_posts([
'post_type' => 'event', // Or whatever your event post type is
'numberposts' => -1,
]);
// Get all the author (user) IDs of all events
$event_author_ids = wp_list_pluck( $event_posts, 'post_author' );
// Now get all the user objects
$users = get_users([
'include' => $event_author_ids,
]);
Alternatively, if you are meaning the author of the current event post, there can only ever be one author per-post, and you can just use the author template tags whilst in the loop.
echo get_the_author_link();
// Get author <a /> HTML
echo get_the_author_meta( $prop );
// Get author property e.g. display_name, user_email, first_name etc.