All-knowingness, or omniscience, is the quality of knowing everything. In the Mr. Deity webseries, Mr. Deity can be all-knowing but chooses to limit his omniscience.
Knowledge of All-Knowingness[]
In Mr. Deity and the Void, El struggles to know if he is all-knowing. He reasons that he does not know if there is anything he doesn't know, and he is unsure whether or not this makes him all-knowing.
On and Off[]
Mr. Deity chooses to keep his omniscience turned off most of the time because "knowing would be no fun". Several times, such as in Mr. Deity and the Intel and in Mr. Deity and the Magic, he is asked to momentarily turn his omniscience on, but he refuses.