Alliance quest is given by [npc=16908] in Stormwind, just outside the northwestern exit of the Dwarven District by the waterfall at 61.33 22.70.
Horde is given by [npc=16926], 34.50 70.80 Orgrimmar at the southernmost bridge in Valley of Spirits.
Picking up this quest will disable it for all other characters on your account, as it's supposed to be a unique item transferable through mail - even cross-realm.
For Starter Edition / unsubscribed players: despite being a level 15 quest, the required item [item=4406] is only craftable at 110 Engineering skill, past the 100 limit of a starter account, and the follow-up quest Crystal Clarity which unlocks the [item=122674] toy for all your characters requires level 30.
Your only chance of getting the scope is by looting it from a [object=19019], which can be found inside some low-level Dungeons. It has an extremely low drop rate however, and according to some sources only the ones in Gnomeregan contain it, meaning you'll probably need a group. The camera will be stuck with the character that completes the quest, as you cannot use the mail and you can't do the quest again on other characters. Better wait until you're subscribed again, buy the scope from the Auction House and then do the follow-up quest aswell.