How do you spell retrained or retraining?

Answer 1

Both are correct, depending on the context.

People must be retrained in a C.P.R. refresher course.

After being retrained in C.P.R., students are certified.

Retraining in C.P.R. takes a few hours.

While retraining for C.P.R., a student had a cardiac arrest which required other students to perform C.P.R. until the ambulance arrived.