If you’re looking to evolve a Sneasel or to increase the chances of your Pokémon to land a critical hit, you want to give them the Razor Claw. It has three locations in Pokémon Sword and Shield.
The first choice we know of at this time is to speak to the merchant who has the chance to sell it, and they’re in Stow-on-Side. They’re the merchant who swaps out their wares every day, so you’re going to want to visit them at least once a day to see what they have to offer. Luckily, they sell that day’s item and the previous day’s option, giving you a chance to make sure you don’t miss what they have for sale if you miss a day.
The second location is the BP shop, which you only have access to at the end of the game. When you beat the game, you can go to the Battle Tower. You can compete against the best of the best in the tower, and you’re going to earn Battle Points. To purchase the Razor Claw from the BP shop, you need 10 Battle Points.
As for the last option, there is a shiny sparkle on an Island in the Dusty Bowl area of the Wild Area that has a single Razer Claw you can pick up. While it is not ideal as you need multiple for evolutions or for areas like the Battle Tower, it is at least one less to collect in the long run.