Relax and destress yourself. This is very simple. You can do it, but not while your head is full of stress and "I can't do this".
The simple fact is that I can't even give you the answer directly because I also don't have any definitive information on the UnsortedType class. Are you sure you really have absolutely nothing on this? If that's the case then I don't see how your tutor can reasonably expect you to complete the assignment and you should IMMEDIATELY raise this issue with him. This assignment is dependent on knowledge of the UnsortedType class and is impossible if that knowledge is nonexistent.
What you would be looking for is some code which starts with "class UnsortedType" and that lists the member variables and functions, including info, length, possibly MAX, maybe one or more UnsortedType constructors, a destructor, maybe RetrieveItem() and other functions.
Earlier you posted some code that started "void UnsortedType::RetrieveItem". Where did you get that from? Did you just make it up; did you hook up /dev/random to a C++ keyword generator, or did you get it from somewhere, e.g. unsortedtype.cpp/unsortedtype.h?
If the function you have to write has the prototype "ItemType ReturnLastItem();" then the outline of the function must be something like:
// some processing needed?
return /* what do we return? */ ;
If any processing is needed it will be to determine which entry is last in the list. At a guess I'd say that was length-1, but nobody it seems knows what length is.
We return something; what will that be, do you think? You can narrow down the possibilities if you have the class definition, because you'd be looking for something of type ItemType, or maybe an array of them.