Q&A for How to Check Friendship in Pokemon Violet

If the woman in Cascaraffa says, "Whoa, you're the best friends ever! I can tell just being together gives you warm fuzzies!", then you can use a Rare Candy on your Eevee during the day (as long as it doesn't know a Fairy-type move) to evolve it into an Espeon. If your Eevee knows a Fairy-type move, it will evolve into Sylveon instead.

A Pokémon caught in a Luxury Ball and given a Soothe Bell will gain happiness fastest, especially if trained on the same route it was caught on.

Eevee evolves into Sylveon by having high friendship, knowing a Fairy-type move, and leveling up.

There's no set amount of happiness points given when you make a sandwich. It depends on the ingredients you use, the Pokémon's Nature, and whether you drop any ingredients while making the sandwich.