You’ll get this quest from Thok, who’s lying injured on the ground across the bridge near Mother’s Heart. The quest is well worth doing as it’ll increase your spear damage. Once you have the quest, follow the waypoint to Arana. When you get there you’ll have a few Watchers to deal with. Take them out with shots to the eye or by using the ol’ dodge and heavy spear combo.
When they’re dead, talk to Arana, who’ll tell you that the Scrapper still has her mother’s spear, but she lost track of it. Use your Focus to highlight the tracks and follow them to find it and a few of its companions. Your job is to kill the one that has Arana’s spear in its side still. Scrappers are tougher than the other machines in the starting area, and require a little bit more care. The best thing to do is to scan it for weakpoints, hit one with your bow, then wait for it to charge you, then dodge, and heavy spear attack. This will knock it down and give you a chance to hit it, or to get a critical hit on it, if that’s a skill you have. Be aware that as soon as you start a fight with the first one, there’s a chance the other Scrappers and the Watchers that are around will all descend on you, so Crowd Control is something you’ll need to be aware of.
When the speared Scrapper is dead, loot it and then take the spear back to Thok for your reward.