van de graaff generator

1.van de graaff generator 其實係positive charge 定係negative charge accumulate on its dome? 係吾係睇情況?

It depends on the design of the van de Graaf generator. Either +ve or -ve charge is possible.

2.假如一個人隻手接觸van de graaff generator D頭髮會豎起 其實係electron 係transfer去個人定係人transfer electron 去van de graaff generator

As said above, this depends on what kind of charge (+ve or -ve) resides on the dome. If electrons are residing on the dome, some of which will transfer to the hair of the person who touches the dome with his hand.