That is a great question. It took a while for me to start really looking at my triggers and often I don't know what they are until I take the time to observe them. What my therapist tries to get me to do when a strong emotion takes over is to be "curious" about what just happened. No judgement, no positives or negatives just like another person observing the situation. That often helps me figure out what just happened, sometimes it has been buidling up and there is a story behind it but having a "childlike curiosity" is usually when I can start to figure it out. By the way this is not easy and takes time.