Lord Elrond has confidence in the loyalty of only one giant, Arifael of Amon Nendir.
'My own scouts did not need to come near to the walls of Helegrod to spy a number of giants on the cliffs over the stronghold. Curiously enough, these giants did not seem to wear the tokens of the Thunder-lord; some new leader must have seized control of this group and sworn allegiance to the power that dwells now within Helegrod.
'I have no doubts to the source of this power: it must come from the Land of Angmar.
'There is one among the giants that I trust still: Arifael on Amon Nendir, friend always to the Elves of this valley. He has always forsaken his more belligerent cousins, though it causes him pain and forces him to live the life of an exile. Amon Nendir is to the south-west of the vale. Speak with Arifael and see if he knows anything about the giants that dwell above Helegrod. I fear that all the giants, save Arifael, are now set against us.'
The giant Arifael is on Amon Nendir, south-west of Rivendell.
Lord Elrond has asked you to speak with Arifael about the giants that have seemingly sworn fealty to Angmar and now protect Helegrod for their new masters.