An omniscient knower would know every true proposition–would have complete propositional knowledge–but would also have complete knowledge de se. He would know, for instance, at each possible world, which world he inhabits; he would know that he is in world W’ when in W’ and that he is in W when in W. But just how he would know this in worlds that are indiscernible–assuming that there are indiscernible possible worlds–is difficult to know. The propositional knowledge God possesses in indiscernible worlds W and W’ would be the same, and so not serve to distinguish W from W’, unless the worlds differed non-qualitatively: unless, for instance, Jones and Smith in W swap bodies in W’; or, unless, for instance, none of the persons in W is identical to any person in W’, despite the indiscernibility of the two worlds. In either case, God would know which world he is in since, for instance, Jones is left handed in W but he is not left-handed in W’.
We’ll say that God is omnitemporal in W only if God exists at each moment t in W. It is among the traditional attributes of God. An omniscient and omnitemporal God would know, at each moment t, in each world W, that he exists at t (not t’) in W (not W’). God knows that he is in W at t, for instance, by knowing everything there is to know at each temporal point t at each world W. The knowledge at each temporal point distinguishes (discernible) worlds from one another. God knows that he is at temporal point t in W, for instance, because he (perhaps) knows that p is true at t, q is true at t-, and r is true at t+, and that occurs only in W. The propositional knowledge at these temporal points serves to distinguish the worlds and inform God of which world he is in.
But now we can see how God would know which counterfactuals of (creaturely) freedom are true. We can see how to resolve the “grounding” problem. God knows that, had he actualized T (the largest state of affairs he can strongly actualize) of morally perfect world W, then Smith would freely do A at t. That’s because God knows that, had he actualized T, he (God) would exist at each temporal moment in T (including the moment t, at which Smith does A). So, had God actualized T, he would know everything that occurs are each temporal moment in T. In particular, he would know that Smith freely does A at t. He would know it, because he would be there to observe it.