Derived demand or joint demand?

It should be derived demand.

Firstly, you should know the definitions of both derived demand and joint demand.

Derived demand refers to the demand for factors of production such as houses and cement.

Joint demand means two goods are used together to satisfy human wants such as DVDs and DVD player.

In this case, the taxi is the factor of the production of taxi service by the taxi driver. Your demand for taxi service is derived from your demand for taxi.

It is not joint demand because when 2 goods A and B are in joint demand, A cannot be used to produce B and vice versa. Just like the example of DVDs and DVD player. Can you use DVDs to produce DVD player?

Hence it is derived demand.

Hope it helps.

Joint demand is the answer.
對生產資料 (factor of production) 的需求是一種引申需求。
For example:
電腦硬件需要適當的電腦軟件才能使用, however they are not derived demand but joint demand.
For 引申需求，一件是 final good (最終物品)，另一件為該 final good 的生產資料；For 輔助品 joint demand，兩者都是 final good。

Taxi and Taxi driver are derived demand for Taxi service.
We can view Taxi and Taxi driver as another sample of DVD and DVD player, i.e. combining it we can watch DVD or have taxi service.

If DVD and DVD player are joint demand,why should we said Taxi and Taxi driver is derived demand?

I don't agree with the answer above.

For taxi SERVICE and taxi driver, they are in derived demand. People demand for taxi service. In order to provide taxi service we demand taxi drivers. That's why the demand for taxi service derives the demand for taxi drivers.

For taxi (the VEHICLE itself) and taxi driver, they must be USED TOGETHER to provide taxi SERVICE to satisfy wants, while either one of them cannot. So they are in joint demand instead.

Joint demand does not mean that one good produces another!!!!