Which fragmented section of the poem, published posthumously, deals with a Titaness challenging the gods for control over the universe?

Correct answer: The Cantos of Mutabilitie

The Mutabilitie Cantos — two complete cantos and a fragment of a third — were published posthumously and were intended for a later, unfinished book of The Faerie Queene. They stage a cosmic trial in which the Titaness Mutabilitie challenges Jove and Nature for sovereignty over the universe.