Alma 18:18

18 Now when the king had heard these words, he marveled again, for he beheld that Ammon could discern his thoughts; but notwithstanding this, king Lamoni did open his mouth, and said unto him: Who art thou? Art thou that Great Spirit, who knows all things?

So Lamoni must have known there was a Great Spirit and that He knows all things, but I guess that was the extent of it.

(I wonder if he was scared of the answers?)