Full Idea
God seems to be in the paradoxical situation that He may be omniscient, but can never know that He is, because that involves knowing that there is nothing outside his scope of knowledge (e.g. another God)
Gist of Idea
An omniscient being couldn't know it was omniscient, as that requires information from beyond its scope of knowledge
Source
PG (Db (ideas) [2031])
Book Reference