CPT is short for cognitive processing therapy, a form of therapy used specifically for clients with PTSD (post-traumatic stress disorder). CPT is an evidence-based cognitive therapy like ACT and CBT. It usually lasts about 12 sessions.
In CPT the therapist will first provide information about PTSD. She will then use questioning and dialogue to help you discover and change the dysfunctional thoughts that keep you from working through and completing the normal recovery process. The therapist will ask you to write about the impact of the trauma and may also ask you write an account of the traumatic event. He will help you process that account. You should eventually learn to identify and change unhelpful thoughts on your own.
If you want to learn more about trauma and PTSD, check out The Body Keeps the Score by Bessel van der Kolk, M.D. A website with tons of information is https://www.ptsd.va.gov/understand_tx/cognitive_processing.asp.
References:
Resick, Patricia; Manson, Candice and Chard, Kathleen. (2016). Cognitive Processing Therapy for PTSD: A Comprehensive Manual. New York: The Guilford Press.
Tull, Matthew; Gratz, Kim and Chapman, Alexander. (2017). Cognitive Behavioral Coping Skills Workbook for PTSD. Oakland, California: New Harbinger Publications.
Van der Kolk, Bessel. (2015). The Body Keeps the Score. Los Angeles: Penguin Publishing.
Williams, Mary Beth and Poijula, Soili. (2016). The PTSD Workbook: Simple, Effective Techniques for Overcoming Traumatic Stress Symptoms. Oakland, California: New Harbinger Publications.