Knowing everything means that for any possible situation or question, you already have the solution. There is no need to involve logic, rational thought, or such. An omniscient being need only be able to perceive, lookup the solution, and act on it.

In other words, it is only a big infinite database. Just as if you were to solve chess, all you'd need to do is encode each posssible position, and when your turn comes up, record the positions of the pieces, and find the corresponding move to bring about the desired result.

Consider it solving reality.