To get an ACF field associated with the user you need to provide the user id in the form of "user_{$user_id}"
or the user object as returned by wp_get_current_user()
$user_id = get_current_user_id();
$value = get_field('field_name', 'user_'.$user_id);
// OR
$user = wp_get_current_user();
$value = get_field('field_name', $user);