There are 13 of Odin's Ravens located in Svartalfheim, although not all will be accessible during your first visit. Afterward, though, all will be available for you to return to and claim later in the game. There is only one Raven in Nidavellir, so, luckily, you'll likely be able to find it on your first visit.
Where to Find Odin's Raven in Nidavellir
Once you reach Nidavellir, the Raven will be near the Odin statue in the town's square. It is to the left of Sindri's shop on top of the smaller roof of a large building, directly above a blue awning. Its color will make it very visible for you to spot immediately.
Note that if you use the Mystic Gateway to reach Nidavellir later on, it will require some backtracking as you won't enter close to the town square. Unlike other Ravens in the realm, this one can be found during your first visits to the area, and does not require an additional quest to access its area.