As everybody else has said, yes you can say "You okay?" But an English speaker would not do this at all times and in all circumstances. It would generally be used in an informal context, usually if the speaker already knows the person he is talking to. "Are you okay?" is already "informal" or colloquial. "Are you all right?" might be considered slightly more formal. But one can also say "You all right?" And please note the standard spelling of "all right." A common nonstandard spelling is "alright," which most teachers would count as wrong.

Yes, that is absolutely possible! If you rescue a person from an accident, you would be very excited and emotional and would yell, "You OK?" You would not "waste" time using the verb.

Maybe, you will find useful the following explanation from a grammar book I use (Michael Swan. Practical English usage. Third edition) 179 ellipsis (3): at the beginning of a sentence 1 words that can be left out In informal spoken English we often leave out unstressed words at the beginning of a sentence if the meaning is clear without them. Words that can be left out include articles (the, a/an), possessives (my, your etc), personal pronouns (I ,you etc), auxiliary verbs (am, have etc) and the preparatory subject there. Car's running badly. (= The car's ) Wife's on holiday. (= My wife's ) Couldn't understand a word. (= I couldn't ... ) Must dash. (= I must dash.) Won't work, you know. (= It won't work ... ) Seen Joe? (= Have you seen Joe?) Keeping well, I hope? (= You're keeping well ... ) Nobody at home. (= There's nobody at home.) Careful what you say. (= Be careful ) Be four pounds fifty. (= That'll be ) This structure is common in advertisements. Two real examples: Thinking of postgraduate study? Call for a place now. (= Are you thinking ... ?) Speak a foreign language? Speak it better. (= Do you speak ... ?) 2 unstressed forms of be, will, would, have We do not usually drop words so as to begin sentences with unstressed forms of be, will, would or auxiliary have (though this sometimes happens in postcards, diary entries and other kinds of very informal writing). I'm coming tomorrow. OR Coming tomorrow. (BUT NOT Am coming tommorow. Am is not stressed.) I'll see you soon. OR See you soon. (BUT NOT Will see you soon. Will is not stressed.) Haven't seen him. (BUT NOT Have seen him. Have is not stressed.) 3 before pronouns: You ready? Auxiliary verbs can be left out before personal pronouns except I and it. You ready? (= Are you ready?) She want something? (= Does she want something?) (BUT NOT I late. It raining?) 4 Dutch, aren't you? Ellipsis is very common in sentences that have some sort of tag (see 487-488, 514) on the end, especially in British English.

Yes you can. It's just like saying "Are you okay" with silent "are".