For po/qen see already pi 1856; for poi= see pi 3068, pi 3069, pi 3070; and for their conjunction see the opening line of Plato's Phaedrus (227A), where Socrates greets Ph. with the twin questions poi= dh\ kai\ po/qen?
The present entry, however, is clearly concerned with these questions not in their original, literal sense but in an applied, philosphical one.
As Adler noted, no specific passage in Aristotle corresponds to the present material. Nevertheless several of his works employ the asyndetic phrase po/qen poi= as a shorthand way of describing the starting-point and the finishing-point of a process or transaction; and (as a TLG search reveals) what the Suda says about it here corresponds with several passages in the Aristotelian Commentaries by Alexander of Aphrodisias. The closest of them is On the Topica 96.19 (on Topica 105b30-37): pa=sa ki/nhsis metabolh\ poqe\n poi= lhpte/on.