Do you mean:
* The highest note sung in Fantasia? This would depend on the specific piece of music, as the film features many different musical selections.
* The highest note played by an instrument in Fantasia? Again, this would depend on the specific instrument and the piece of music.
* Are you looking for the highest note achievable by a specific opera singer or musician who has performed in Fantasia? Please provide more context about the specific person you're asking about.
Please clarify your question so I can give you a more accurate answer.