The artifact Book of Exalted Deeds (DMG, p. 222) has the following attribute:
Enlightened Magic. Once you've read and studied the book, any spell slot you expend to cast a cleric or paladin spell counts as a spell slot of one level higher.
How does this work for cantrips, since there is no real level to increase it too? Does the cantrip just do extra damage as if it were cast by a higher-level character?