To get the Grossmesser curved sword in Elden ring, you will need to slay skeleton enemies who use curved swords just like it. But slaying just one skeleton won't be enough to get the Grossmesser because the drop rate can be rare. Because of this, you will need to farm skeletons for the sword. To farm skeletons, you need a high Item discovery rating. You can get high discovery by either using Silver Scarabs or having a high Arcane Stat.
Having high Arcane raises the base Item discovery rating, while using Silver Scarabs increases it for a short time. Using a combination of both high Arcane and Silver Scarabs is generally the best way to go. Doing so will also increase your Item discovery the most, which will help you get a Grossmesser loot drop faster.
Where to find Grossmesser in Elden Ring?
If you want to find the Grossmesser, you will need to farm the skeletons that spawn in Tombsward Catacombs. Inside Tombsward Catacombs, you can find large skeletons, some of which wield curved swords. Farming the skeletons carrying the swords will eventually get you the Grosmesser in Elden Ring. That said, if you what to find Tombsward Catacombs, you can do so in the location shown below on the Weeping Peninsula
For more on Elden Ring, Pro Game Guides has you covered!