The inquiry-science taught by the sixth avatara
'Anvikshikim... ucivan' (SB 1.3.11).
आन्वीक्षिकी
Anvikshiki is the 'science of inquiry' of ancient India's curriculum — reasoned examination of truth, counted among the classical vidyas in the Lokayata-Chanakya tradition. In SB 1.3.11 Dattatreya taught precisely this to Alarka and Prahlada and the rest.
Śrīmad Bhāgavata Mahāpurāṇa 1.3.11 — Sanskrit Wikisource (pinned oldid=369178)
'Anvikshikim... ucivan' (SB 1.3.11).