You can get this quest by speaking to Grelin Whitebeard located in the second encampment on the road southwest of Anvilmar. Speak to Grelin and he will say:

My brother Senir and I were sent to different parts of Dun Morogh to investigate the threat posed by the trolls. The Senate has its hands full with the troggs, so they've no need for further annoyances.

From what I've seen, the trolls aren't well situated here in Coldridge Valley--mostly the southern cave. I'd say that the army will not be necessary. A few strong arms should be more than enough.

Perhaps you'd like to assist in this endeavor? I have the authority to offer compensation for your help.

Kill 14 Frostmane Troll Whelps

The trolls are pretty easy to find, you can either go to one of the camps located south of Grelin or venture into the cave he mentions, south of him. Here you?ll find Frostmane Troll Whelps (level 3-4), they?re not that tough, so with a little patience you will soon reach your goal. This quest is a good one to combine with A Refugee?s Quandry since it will involve visiting the troll camps anyway. When you?re ready, speak to Grelin again.

Argh! Those light-blasted trolls!

lt; He takes a few breaths and seems to settle down?a bit gt;

A group of them came in the night and stole my journal! I knew better than to trust a good-for-nothing appr?

Well as you can hear, Grelin is pretty upset about something, so hurry and choose your reward before he explodes. Accepting the next quest The Stolen Journal would probably cool him down a bit.