I am sri lanken citizen. Live in Sri Lanka and not a Tax payee in Sri Lanka (i.e not sufficient income to pay tax)
I want to get a prize/services money from USA .
Do I need to get ITIN number form USA IRS?
Do my money will get detected 30% tax from USA?

The 30% withholding would be the amount of the tax you would pay. If the company that issues the prize withholds that amount and does not require you get an ITIN, then you need do nothing, as the tax is already paid and nothing is gained by filing a tax return.

I am not living in USA and not a USA citizen.

(I am)The beneficial owner is a resident of Sri Lanka within the meaning of the income tax treaty between the United States and that country.

So what is the percentage of tax I have to pay?

Do I have Special rates and conditions ? If so
How can I Explain the reasons the beneficial owner meets the terms of the treaty article:

Not sure.

HOW MUCH is the prize in U.S. dollars??

Us$ 200

Under Article 12 (Royalties), the withholding rate is 10%.

Under Article 10 (Dividends), the withholding rate is 15%.

Bother are LESS than the default 30% withholding rate. Submit W-8BEN and cite Article 12 to get the withholding rate reduced to 10%.

This is for, I got price money $200 from a online software competition, will it come under Article 12?

what can I explain for , Explain the reasons the beneficial owner meets the terms of the treaty article in the W-8BEN form:?

Article 12 is the closest I can determine the prize money falls under.

Claim the 10% withholding under Article 12. No other explanation is needed.