Well, the most simple way to find if a person speak English or not, is to ask them a question in English, such 'Do you speak English?' If they can not understand that, then its definitely a NO.

'Do you speak English?' can be translated as '你会说英文吗?' in Chinese. It is pronounced as nǐ huì shuō yīng wén ma ?

你 (nǐ) , the third tone, means you;
会 (huì ), the fourth tone, means can, or able to;
说 (shuō), the first tone, means speak;
英文 (yīng wén), the first tone and second tone, means English;
吗 (ma), light first tone, is often used at the end of a question.

You can watch the video here to learn how to start a conversation with 'do you speak English' in Chinese. www.atozchinese.com/lessons/beginner/Do_you_speak_English

Hope it helps.