$current_user = wp_get_current_user();
$user_email = $current_user->user_email;
xxxxxxxxxx
$user_info = get_userdata($userID);
echo $user_info->last_name . ", " . $user_info->first_name. ", " . $user_info->user_email;
xxxxxxxxxx
global $current_user;
get_currentuserinfo();
echo $current_user->user_email;