Solution:
- 1. This is the shop where I bought my new headphones. ('Where' is used to refer to a place).
- 2. The man whose car was stolen is very upset. ('Whose' indicates possession).
- 3. Summer is the season when we all go on holiday. ('When' refers to a time/season).
- 4. I have a friend who lives in a small countryside village. ('Who' refers to a person).
- 5. This is the skateboard which my brother gave me for my birthday. ('Which' refers to a thing).
Final Answer: 1. where, 2. whose, 3. when, 4. who, 5. which