Dreams involving themes of travel, betrayal, and injury can be quite complex and often reflect deep emotional experiences or conflicts in waking life. Here's an interpretation of your dream:

1. Traveling on a Train: This could symbolize your journey through life, with the train representing the path you're on. The fact that you're traveling from the city to the country may suggest a desire for peace or a return to simpler times.
2. Mother-like Figure: This character might represent nurturing qualities or guidance, but her sudden betrayal could indicate feelings of hurt or disappointment from someone you trust in your life. It could also represent unresolved issues with a maternal figure or authority.
3. Being Stabbed: The act of being stabbed may symbolize a feeling of betrayal or emotional pain inflicted by someone close to you. The location of the injury (waist/pelvic area) might suggest that this pain is deeply personal and related to your sense of security or identity.
4. The Knife: The yellow katana could represent a sharp, painful experience that is difficult to remove from your life. Keeping the knife inside you might indicate that you feel you have to carry the burden of this pain, which could be affecting your health or well-being.
5. Cancer: Developing cancer from the knife could symbolize the long-term emotional or psychological consequences of this betrayal or pain. It may represent fears about how unresolved issues or past traumas can manifest in your life.
6. Speaking at Schools and Conventions: This aspect of the dream suggests a desire to share your story, perhaps indicating a need for healing or a way to process your experiences. You might feel compelled to help others who have faced similar struggles.

Overall, this dream may be urging you to confront emotional pain or betrayal in your life. It might be beneficial to reflect on your relationships and consider if there are unresolved issues or feelings of betrayal that need to be addressed. Seeking support from trusted friends or professionals could help you navigate these feelings.