One wild cart ride later they stood blinking in the sunlight outside Gringotts. Harry didn't know where to run first now that he had a bag full of money.
(Harry Potter and the Sorcerer's Stone)
"Now that" means since. Then the highlighted sentence can be replaced by "(1) Harry didn't know where to run first (2) since he had a bag full of money." Semantically, this is somewhat awkward; I think that (1) cannot be the consequence of (2).
What's the exact meaning of the highlighted sentence?
The core sense of now that is that now, in the present, one thing has been accomplished, and what follows—the “consequence”—is in operation in the present, and/or lies ahead, in the future. But what is in the future may or may not be known; and now that is very often used in situations where it is not known.
Now that he had graduated, he was ready to look for a job. OR
Now that he had graduated, he had no idea what he would do next.
Harry's case parallels the latter: this thing is done, what is the next thing to do?
StoneyB's answer is correct, but some additional examples that are equivalent to now that may help. (That is, these examples and variations upon them can substitute for now that in the sentence in the question without much altering the meaning.)
• it now being the case that
• it being the case that now
• present circumstances being such that
