1. What do we call a period of 1000 years？

Millennium /məˈlɛniəm/ 千禧年

2.  In a figure of hexagonal, how many sides does it have? 

Six （hexagonal 六边形 /hɛk'sægənl/）

3. A specialist who repairs leaking water pipes is called as? 

Plumber 水管工 /'plʌmə/