Pour water and chicken broth into a saucepan; stir in the garlic and bring to a boil. Stir in pearl couscous, cover the pan, and remove from heat. Allow couscous to stand until water has been absorbed, about 5 minutes; fluff with a fork. Allow couscous to cool to warm temperature.

Lightly toss couscous, chickpeas, sun-dried tomatoes, olives, and feta cheese in a large serving bowl.

To make the dressing: Mix white wine vinegar, lemon juice, oregano, and black pepper in a small bowl until well combined. Pour over couscous mixture; toss again to serve.