You could check them each for signs of laying:
https://www.backyardchickens.com/articles/who-is-laying-and-who-is-not-butt-check.73309/
Or you could separate them for a few days, and see who lays eggs. Putting one in a wire dog crate, inside the area with the other one, would let them still interact (so not as lonely), and you will soon know who is laying. If you do this, keep them separate until you have at least two or three eggs.
Since they are 3 years old, and they are of a breed known for being good layers, my guess is that they are both laying, but fewer eggs than when they were younger. If each lays one egg every two days, they could lay on alternate days, which would work out to one egg each day.