Only as many as you want to. According to EMDR originator Francine Shapiro, “with other forms of therapy, you have to describe the memories in detail. With EMDR therapy, that’s not necessary. The client says as much or as little as they want to. As a matter of fact, in many instances, you can do it content free…”, http://www.psychotherapy.net/interview/francine-shapiro-emdr
In EMDR therapy, once processing has begun, the therapist actually says very little. The only thing required from the client is some kind of cue letting the therapist know that things are moving in the direction the client has chosen. An EMDR therapist intentionally gets out of the way of the client’s ability to move through the pertinent material, allowing connections to be made internally and realized by the client for the best healing experience.
For me, one of the best parts of doing EMDR with a patient is watching the client’s face as the change takes place. Seeing that liberation from such deep pain and fear to a new place that is peaceful and empowering is quite remarkable.