Scrub potatoes and cut crosswise into 1/4-inch-thick slices. Lay potatoes on a rack in a pan over at least 1 inch boiling water. Cover and steam potatoes over medium-high heat just until tender when pierced, 10 to 12 minutes.
Meanwhile, pat dough evenly to fit a lightly oiled 12-inch pizza pan.
Scatter mozzarella and jack cheese over crust. Lay potato slices in a single layer over cheese. Lightly sprinkle potatoes with salt and pepper. Scatter rosemary, onion, capers, and feta over pizza. Drizzle with 1 tablespoon olive oil.
Bake on lowest rack in a 500° oven until bottom of crust is well browned, 12 to 15 minutes for bread dough, 9 to 10 minutes for pizza crust dough. Cut into wedges.