Hilund at the Thirsk Mead Hall asks of the Dragonborn to retrieve 50 Riekling spears for her. The spears are plentiful where Rieklings can be found, like Frossel for example. Hilund will reward the Dragonborn a leveled amount of gold for retrieving the spears. After delivering the spears to Hilund, they will be displayed outside Thirsk Mead Hall after a few days.
If you're feeling a bit cheeky, then you can also keep dodging the spears a single Riekling throws at you until you get all 50. Takes longer, but it can be more entertaining.