Driving with a learner's permit and pulled over, who's at fault, the student (18+) or the instructor?

the driver has some responsibily and so does the intrutor , after all you doing as the instructor says , but you must show responsibilty too .

The driver is responsible.

I would say Instructor.  Really depends on the circumstance.  The instructor has a "full driver's license" so he is suppose to know the rules of the road.  A learner is IGNORANT.  So it generally does not happen.

The person driving........

The driver.  Whoever was driving.

Who  got the ticket?

Whoever the officer puts on the ticket.  Probably the student.

Why were you pulled over? That could have a lot to do with who is at fault. Maybe at fault would be if you were following instructions from the instructor or not following instructions.. 

the fully licensed driver will be getting the fine as its their licence the learner is driving on. To have a full licence in most places you'd be 21. I'm Australian  it may be different in other country's.

Possibly, no one. Most police won't issue a ticket in that situation because it would almost certainly mean the learner won't be allowed to get their license. 

That said, who is at fault would depend on the circumstances. A police officer could find that the fault is solely that of the learner, like the learner was disobeying the instructor, and so only issue the learner a ticket. A police officer could find that the fault is that of both the learner and the instructor and issue both of them tickets. Never will the officer find the instructor alone is at fault because the learner with a learner's permit had to demonstrate sufficient knowledge of driving and traffic laws to get a learner's permit and so the learner, being the driver, is always going to be at fault for any traffic violations.