When forming a question in English, there is what is "correct" and what is more or less formal. Firstly, you should review how questions are normally formed in English, because there are several different types.
Dropping the auxiliary verb or using statement order instead of question order is sometimes done in informal speech, but it's more complicated than that.
a) Are you Ok? b) You ok ?
In this case, a) is correct and formal, and b) is correct in informal speech.
a) Did you see that movie? b) You saw that movie ?
As with your first example, a) is correct and formal, and b) is correct in informal speech. It's an example of using statement word order as a question.
a) When did you see that movie ? b) When you saw that movie ?
In this case, though, a) is correct and formal, and b) is never correct (except in some dialects). When asking a when-question, we always use an auxiliary verb if there is another verb in the sentence: When was the festival? but When do you eat? When will they arrive? When did she write her book?
a) Who did give you this? b ) Who gave you this ?
Here, a) is only correct as an example of the emphatic do, and b) is the normal question form. You would only use a) in a case like
Did Mike give you this? No? Well then, who did give you this?