Lufthansa lounge is in the North terminal next to United and Lufthansa gates (it's between D6 and D8). It's open around 1:30-5:30pm daily. (Probably not much use to you if you depart on a CO flight due to its location).

All you need is your star gold card (physical card needed) and a BP for a star alliance flight (domestic economy is fine). Your PC membership is entirely immaterial (and does not grant you access). (The only other domestic LH lounge is in IAD, B terminal - same rules apply, although their hours are slightly better.)