The correct form is: How long have you been studying (for)? The other one is: How much have you studied? How far have you studied (to)? You should learn these.

1.If your english meaning is "(you started in the past and you're not longer studying it anymore)",it is a pluperfect. The answer should be:你学过多久的英语？(or 你学过多长时间的英语) 2.In Chinese the aspectual particle"过"after the predicate verb is used to express a certain experience in the past,.and the experience didn't continue anymore. e.g.我做过两年的医生。(I had been a doctor for two years) It indicates that "I didn't worked as a doctor in some past time anymore" e.g.你和他交往过几年？(how long had you been in love with him?) It indecate that"you were not in love with him in some past time anymore" 3."了"only shows that an action is in the state of completion.If the time is not specifically pointed out,generally it refers to "the present","the time of speaking" e.g.你学了多久的汉语（How long have you studied English for? ） This is a present perfect,means you are still studying English now.

How long have you been studying English? 1、你学习英语多久了？ 2、你学了多长时间的英语？ 3、你英语学了多长时间？ you started in the past and you're not longer studying it anymore 你之前学过，但现在你已不再学习它了