If I understand your question, it looks something like this:
- God on the B-theory is outside of time.
- To be outside of time is to be incapable of experiencing changes
- To know something requires experiencing change.
Clearly, this set is contradictory. In fact, it's plainly so. The fact it's plainly so should be a hint that this is an incorrect reading of someone's philosophical position.
Simply put B-theorists about God's relationship to time reject claim 3. For them, to know something in the case of God is dissimilar to knowing in the human case.
For humans (and temporal beings), knowledge has a feature of coming to know, but there's no reason why this is necessary. For the B-theorist, God has instant knowledge of everything throughout eternity as if it were a single moment.
To give an analogy using a movie's physical film, temporal beings have an A-theory experience of time wherein each frame happens in sequence and there are frames before the current frame and after the current frame. There are things we come to know in future frames, etc. Similarly, we come into and out of the film and experience all sorts of states (sinus infections, births of children, etc).
Conversely, a B-theory God sees every frame of the entire movie all at once as if in a single instant. This God doesn't experience any of this as passage. It all just is. In other words, that person Q has a sinus infection at moment 33331 is part of the knowledge for b-theory God but b-theory God has no moments and does not pass through time. For a person in time, the sinus infection begins at say moment 33330 and ends at 33338.
The basic idea is that God knows from eternity (here understood as neither before, during, nor after events) what happens at each moment of time regardless of whether we as temporal beings see these as "past", "present", or "future."
For more, you can read http://www.iep.utm.edu/god-time/#SH1b.
To simplify, if you find this account of B-theory knowledge (eternal knowledge or an eternal being behind it), then you probably would simply reject either that any God exists or that the existing God is a B-theory God.