Thank you for your question. The idea of knowledge which comes from Allah through metaphysical means, rather than through normal means of acquisition has been derived by Muslim thinkers reflecting on verse 18:65 in which Khidr is described as having this trait.
If the definition of ilm al-ladunni is as mentioned above then revelation is the highest form of this type of knowledge, followed by hadith qudsi and then other types of mystical experience. We have plentiful reports about such types of mystical experiences occurring in the life of the Prophet (saw) and the Imams (as). If it seems incoherent that the knowledge of the Imams (as) is only acquired from their study of the Prophetic sunna, then a reasonable explanation would be some level of ilm ladunni. Some commentators have explained ilm al-ladunni as prophethood, and Allah knows best.
May you always be successful