If you are trying to access the current user's info on the server-side (in PHP), you can directly access the object. For example,
echo $loggedInUser->user_id;
echo $loggedInUser->email;If you need to access it the user's information from the client-side, i.e. in Javascript somewhere, you can get this information from api/load_current_user.php. For convenience, there is a Javascript function loadCurrentUser(), that will load information for the currently logged-in user. It can be found in js/userfrosting.js. This function returns a JSON object containing the user fields.