Student or Learner
In question form, I would ask: "How long have you received private tutoring?".
Can I say that I am asking for the "length of time of receiving private tutoring"?
They're both fairly unnatural. In fact, the second is incorrect.
How long have you been having private tutoring?
For how long have you been privately tutored?
You are asking for "the length of time the person has been receiving private tutoring".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.