The correct phrase is "interested in," not "interested on." This represents a standard collocation in English where "in" is the appropriate preposition to pair with the adjective "interested."
When expressing curiosity, engagement, or enthusiasm about a subject, activity, or concept, we always use "interested in." For example:
- "I'm interested in quantum physics."
- "She became interested in photography last summer."
- "They aren't interested in the proposal."
This usage is consistent across all forms of English (American, British, Australian, etc.) and applies in both formal and informal contexts.