Is there any provision for subcategorization?/ If   I have sub categories present within my main categories, will the prediction also be made on the sub categories while running the AI Classifier?

Yes, there is video Tutorial named Projects, in that video tutorial you can check how the Subcategorization can be created. Also, although while selecting the categories for the AI Classifier to run on , just Main Categories are shown, however, if you have subcategories within those main categories then the predictions will also show-up into any of the sub-category based on the training data and the threshold you have selected.