There is an online English class room which has an increasing number of teachers, most of whom I don't know at all.
I have to book a room by time, e.g. 8 pm Wednesday, to attend class. I don't know who will be assigned to that classroom before I booked a room successfully.
To convey the same idea, should I say
I don't know which teacher will be assigned to me
I don't know what teacher will be assigned to me