Abridged from Harpokration (and Photius) s.v. Besides Aeschines 3.82, cited there, the place -- briefly prominent in the history of the third quarter of the C4 BCE -- is mentioned by Hegesippus in [Demosthenes] 7.37 and by Demosthenes himself (responding to Aeschines) in Demosthenes 18.27.
Ergiske does not feature on any map in the Barrington Atlas; however, in the context of other place-names with which these orators associate it (such as Serreion Teichos [sigma 250] and Doriscus [delta 1384]), it was on or near the Aegean coast of eastern Thrace; consequently it should probably be located on either map 51 or map 52 of the Atlas.