Can a Chihuahua eat olives?
Better to avoid. Far too salty.
How much: If he eats one pitted olive by mistake, it's no big deal. Don't give them as treats.
Why
Jarred olives are extremely high in sodium. The pit is a choking and blockage hazard. If you want to add healthy fat, a drop of olive oil is better.
Olives in a Chihuahua's diet
Keep in mind how tiny the portions are for this breed: an adult Chihuahua eats roughly 1 to 2.3 ounces (25-65 g) of food a day depending on his weight, and treats shouldn't go over 10% of his daily calories. That's only a small fraction of an ounce. What looks like "a little bite" to us can be half a meal for him.
This information is for general guidance and is not a substitute for advice from a licensed veterinarian. Every Chihuahua can react differently; if in doubt, always check with a professional.