If this is your definition of subtext:

“Subtext in writing is the underlying meaning or message conveyed by a text that is not explicitly stated by the characters or shown in the narrative. It’s the layer of meaning that lives beneath the surface dialogue, action, or plot, offering depth and complexity to a story. Subtext can be created through dialogue, character actions, symbols, and the overall context of the story, allowing readers or viewers to infer deeper meanings and emotions that aren’t directly expressed. It enriches the audience’s experience by engaging their intuition and imagination, inviting them to read between the lines to uncover the true essence of the narrative. Subtext can reveal character motives, thematic elements, and emotional undertones, making the storytelling more nuanced and resonant.”

Then yes, you absolutely can train an AI on it. I already did and it’s called Subtxt. The app is trained on the underlying meaning of a story, not the text itself, and is designed primarily to help authors discover and refine the message of their work.