Sure, here are the correct pronouns to complete the sentences:

1. This is the restaurant **where** I first met my husband.
2. July and August are the months **when** most people go on holiday.
3. Do you know the reason **why** she left so early?
4. This is the school **where** I and my best friends attended.
5. This is the town **where** the greatest leader of the country came from.
6. 14th February is the day **when** lovers exchange their gifts.
7. Becoming rich is the reason **why** so many people work like crazy.
8. A supermarket is a shopping center **where** you can buy almost anything.
9. The day **when** he arrived was very nice.
10. A plane crash was the reason **why** I couldn't sleep last night.

I hope this helps!