Do I need hotel reservation if I apply for a visa to China in Korea? I have a friend there who will let me stay.

Yes, hotel reservation is required by the embassy for applying a China visa. A few days of the hotel reservation is enough, not necessarily for your whole stay in China. However, if you’ll stay in your friend’s, you can submit an invitation letter from your friend instead, stating she will offer accommodation during your stay in China, the address of the accommodated place and a copy of her China resident permit and passport. Other requirements include:
1. Applicants' original passport
2. One properly completed Visa Application Form with one recent passport photo attached on it. Applicants should write clearly their address and telephone on the Visa Application Form. If applicants want to stay in China for more than 30 days, please write the name, address and telephone of their relatives or friends in China.
3. Two-way flight tickets.
4. Alien Registration Cards.