You simply need to tap off the wiring for the existing outlet using pigtails (short pieces of wire of the same weight and color).
Run a new 14/2 cable from the combo box to the new outlet location. Remove the hot lead (probably black) from the side of the existing outlet. Connect that lead to the black of the new cable and to the black pigtail using a wire nut or a push-in connector. Attach the other end of the black pigtail back on the hot terminal of the combo outlet.
If the hot wire to the combo outlet is already connected through a wire nut, you just have to add the new black to that bundle and reattach the wire nut (or a bigger one if necessary), no new pigtail needed.
Do the same for the neutral (white) wires. White to white.
Connect all ground wires (bare or green).