Do I need visa to go to China for 4days?

You need A No-objection letter from your company stating your position ,monthly or yearly salary, it is required for Chinese visa application.

You also need to apply for a China visa through China consulate in Dubai. Can you tell me the purpose of coming to China?

just to visit my friend

But i have Ukrainian passport

The complete requirements for you to apply a tourist visa to visit your friend are:
1. Original Ukraine passport

2. UAE resident visa valid for more than 6 months.

3. China visa Application Form V.2011A and V.2011B

4. One passport photo

5. Copies of the data pages of your passport and UAE resident visa.

6. A No-objection letter from your company

7. Invitation from your friend in China with a Copy of his passport & residence visa;

if i go only to Hong Kong do i still need visa?

Ukraine passport holders are exempt from a visa to Hong Kong for up to 14 days, you don't need a visa to Hong Kong.

Thnks a lot!!!!