What jazz pianists mainly do is not write chord symbols for given notes. It's the other way around: what they do is, look at already written chord symbols (or even better, know the changes without staring at a music sheet) and make an artistic contribution by coming up with notes. Or a jazz pianist may even improvise everything about the chords and their realization, but now you're reading a book that has chord symbols and staff notation. If the book is about jazz piano, written for aspiring instrumentalist, then I think the examples in the book should be looked at like this:
The chord symbols do not try to be a theoretical description of the notes. And the notes don't try to be a theoretical explanation of what the chord symbols mean. The notes are an example of one possible practical realization of the chord symbols. And not just practical, but even an artistic, tasteful realization that the player subjectively likes.
What comes to this particular book, The Jazz Piano Book by Mark Levine, the author has in a way formalized the jazz practice of approximating "official" changes and improvising the final details on the fly. Whatever kind of major chord it is, if it's not a dominant chord, Levine uses ∆ as a generic symbol. Quote from the introduction of the book: (which I recommend reading, if you're using the book)
The unhappy fact that the chord symbols C, C∆, Cmaj7, CM7, C6, and C69
all mean pretty much the same thing and are often used interchangeably
can be discouraging to a beginner. In this book, I’ll use the ∆
symbol for all major chords.
(Note how that confusing and unusual notation was intended to be good for beginners!?)
And since this is now the accepted answer, I'll adress your question just to make it clear.
How am I supposed to tell that this is really a G7b9
Like explained above, "G7b9" meant something that was assumed to be given in the lead sheet. Or actually, even an approximation of what there might be in an actual lead sheet, since Levine combines many chord types under a generic symbol like ∆. So, whatever notes are written on the stave, that's Levine's artistic choice of what you could play - and he chose to use a rootless voicing in his example.
To understand Levine's enharmonic spellings, you need to know how he selects scales to use, and the spellings may not be based on the key signature of the current key. It's explained in the book, but an example is in the question Db in realization of "A7alt" in Levine's piano book
But that's not all. The spelling of b9 of G7b9 as G# does not follow Levine's own logic. Look at Figure 9-28 on page 76. If you should equate the G7b9 chord with a G half-whole diminished scale, then there is no G# in that scale - if written according to how Levine presents it in chapter 9. But the G# is not a bad thing, because it lets you clearly see the E major triad there. Which might be why Levine made the mistake of not following his own scale system. Maybe he simply looked at the notes as an E major triad and wrote down what he saw.
EDIT. The following is my original thoughts about the G# spelling, before reading the book:
What comes to the enharmonic spelling of the G# note, if it's "b9", shouldn't it be an Ab? I see that E major triad as something that a jazz player would actually think about, a pianist, guitarist or a sax player just the same. When you see the chord symbol - a dominant chord - you might think "I'll play a major triad rooted a minor third below the dominant's root". So: you see "G7", you play an E major triad over it. If you want to advice the reader to look at it as an E major triad, then the spelling E - G# - B is exactly right and proper and correct.
If you think about a half-whole diminished scale over a dominant chord, which is a common style in jazz, then you can take any chord that's found in the scale and move it up and down in steps of three semitones, and you'll stay within the diminished scale. For example, take a G major, you can move that in steps of three semitones: G major, E major, C# major, Bb major. Worrying about "correct" enharmonic spellings for these is completely missing the point of what you should be thinking about here. In any case, as a jazz soloist, you're trying to make the listener feel ambiguous about the harmony and come up with things that could enharmonically exist in many different keys although maybe with different names ... the final "correct" spelling, with the advantage of hindsight of knowing where the harmony actually eventually went, might be different from how it's good to think about it while playing.