The sconce dimensions don't add up. It says the shade is 8' deep and the overall fixture is 8" deep. One of those is wrong when looking at the side view.

I think 2 sconces look better in the space.

I think 8" refers to the overall diameter, and 10.75 is how far it comes from the wall with the gooseneck?

I'd choose One.

One would be sufficient for a 50" window, plus task lighting under the cabinets. The fixture is lovely, BTW.

One would not be sufficient nor would it be balanced. In design we want to create that balance, with even proportions. So going with two sconces will give you a "balanced and completed" look and feel.