You are the 'qualified' crew member and therefore you log the hours as Co-Pilot. The trainee is
NOT qualified to act in the full role until signed off by a training captain. Therefore, in the event of an emergency, he will be ejected and you will be inserted into the RHS to conduct the duties for which you are carried.
Have fun
p.s. You should also get any sector pay attributable to the training sectors. Always check
W2P