For the residence registration, in case of lost passport or maybe to report someone you might have to go to the police station. Here is a list of Police Stations (Paichusuo 派出所) in the vicinity of Wudaokou:
Dongsheng Police Station (东升派出所)
21号 Chengfu Rd, Haidian, Beijing, China, +86 10 6231 1235 , +86 10 6231 7177
Dongsheng Police Dizhi Daxue Station (地质大学第一社区警务工作站 )
Also please note that there are Police Duty Boxes on the southwest and north east side of the crossing of Chengfu Lu and Heqing Lu, right in front of the Wudaokou station. Since there are so many bars and clubs in the area where you might run into trouble, you can go there for help if you need it!