Yes, they all have same meaning. But honorific level is different. Korean is honorific language. There are 4 honorific levels in korean. You may be dizzy with it. kkkk If you are saying to older person and you have to say in formal way, you should say "영어를 하실 수 있으세요?" if he is just a stranger or you don't need to say in not formal way, "영어를 할 줄 아세요?" or "영어를 할 줄 알아요?" if he is your friend, just say "영어할 줄 알아?" Find your korean teacher! Korean is never easy.

There are a few different things going on in your examples. First, the two similar but not the same expressions: - 할 줄 알다: know how to do something; have the skill to do something. - 할 수 있다: can do something; have the ability to do it. The different sentence endings are just variation in speech style and politeness level, with no change in meaning. Here's a heads-up: * Speech style (informal vs formal) and politeness level(casual vs polite) - informal: smooth style - for friends, family, and anyone familiar. - formal: stiff style - addressing a multitude or strangers, or writing impersonally. - casual: plain (without politeness added) - for familiar people roughly your age or younger. - polite: respectful - for those who are senior to you in age/position. In daily life, informal-casual style is the most common, followed by informal-polite. The formal styles are mostly for public addresses (radio and TV broadcasts), formal speeches, and the like. Speech style is not something rigid and fixed, however. A mix of two or more styles may be used in the same conversation. Examples (using only the present tense). 이다 (is/am/are. special verb/particle): 1) 이야/야: informal, casual. 나는 학생이야. 2) 이에요/예요: informal, polite. 저는 학생이에요. 3) 이다: formal, casual. 나는 학생이다. 4) 입니다: formal, polite. 나는 학생입니다. 같다 (the same, like. adjective): 1) 같아: i-c. 날씨가 추운 것 같아. 2) 같아요: i-p. 날씨가 추운 것 같아요. 3) 같다: f-c. 날씨가 추운 것 같다. 4) 같습니다: f-p. 날씨가 추운 것 같습니다. 하다 (to do, perform. verb): 해 / 해요 / 한다 / 합니다. 춥다 (cold. adjective): 추워 / 추워요 / 춥다 / 춥습니다. 먹다 (to eat. verb): 먹어 / 먹어요 / 먹는다 / 먹습니다. * For adjectives, the formal-casual form is the same as the root form (같다, 춥다). There are also corresponding question forms: 이다 - 1) 이야? (same as the indicative form), 2) 이에요? (same), 3) 이냐? 4) 입니까? 같다 - 1) 같아? (same), 2) 같아요? (same), 3) 같냐? 4) 같습니까? You also have honorific forms of verbs in some of your sentences. 가시다 is an honorific of 가다. 아시다 (in 아세요) is an honorific of 알다.

영어 할 줄 알아요? (a) 영어 할 줄 아세요?(b) 영어 하실 수 있으세요?(c) ----These are no differences in meaning. However ,just in my opinion, C is the most honorific form of them. And A is the lowest one. 영어 할 줄 알아? Same meaning, but Only for the younger or friends

Thank you for the reply. Then do they mean anything slightly different? What is the difference in vocabulary? Does it suggest some different level of capability in speaking or something?

That is 영어를 할 수 있습니까? I think you should know Korean forms are different depending on whom you are talk to. The forms are usually divided by if they are older or younger than you. 영어 할 줄 알아? can be said for people younger than you and the same aged friends usually. 영어 할 줄 알아요?, 영어 할 줄 아세요? 영어 하실 수 있으세요? and 영어를 할 수 있습니까? can be used for all people.