Use google or bing; works better than internal search.
If it hasn't changed in the newer versions; the below are cut and paste from some searches I did.
The member id of the member currently logged in can be pulled from the cookie.
$memID = $_COOKIE['memberID'];
The members nickname can be obtained by passing the member id to the dolphin function getNickName $nick = getNickName($memID);
The function getLoggedId() will also return the ID of a member logged in. It's like pulling it from the cookie.
There is also getIdByNickname($nickname) which returns the member id of the passed nickname.
Also be aware that some of these function calls will not work on every page. It all depends on what php classes are included on that page.
So you really should be looking at the php classes for dolphin located in the inc and inc\classes folders. This is where you will find all this stuff.