In citing works by Plato scholars traditionally use a number system developed especially for this known as Stephanus Numbers. Below are some articles that describe Stephanus Numbers and how to use them.
"Quoting Plato: Stephanus References"
In this article Bernard Suzanne says including line numbers is only done "in some instances," meaning they are not always necessary. Line numbering taken from translations can only be approximate.
Just in case you are a curious overachiever, directly below are links to each of the three volumes of the Stephanus edition of Plato's Works. Of course, it is in Greek. If you can read it, you are probably already a scholar dealing with ancient texts and do not need this guide!

Head of Plato. Roman copy. Photo by Bibi Saint-Pol. Wikimedia Commons
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