There are around eight disciplines for Subject Tests in GRE depending on your area.
Usually conducted thrice in a year in October, November & April.
- Learning and motivation
- Cognition and human learning
- Physiological and Comparative Psychology
- Sensation and perception
- Developmental psychology
- Abnormal psychology
- Clinical psychology
- Personality psychology
- Social psychology
- Applied psychology
It's a multiple choice format exam with around 200 questions
Official Webpage for Test Pattern
GRE Psychology Test Preparation Official Book
I hope this information will be usefull for you so all the best for exam.