Find a clue as to the gems' whereabouts in the depths of Uldaman.
As sure as Malton is a dummy, those gems are still in Uldaman somewhere. You're going to have to go back there and look for them.
Like I said before, if the information we have is correct then there's a ruby, a sapphire, and a topaz that go with the necklace. Find them and put them in the necklace.
As to where the gems are, who knows? Maybe you'll get lucky and find the corpse of the Paladin. If he's not been stripped clean already, then maybe he's got them on him still.
You seem to have found the remains of the paladin that Dran had mentioned from before. Searching the remains uncovers what would appear to be his journal. The book is in poor condition, as dried blood has stained most of the text in the book. What you can read, however, is gibberish; it is written in the native tongue of the humans, to the best of your knowledge.
You will need the book translated if you are to glean any knowledge from it.