Abydos is near El Balyana in Sohag Governorate, roughly 150 km north of Luxor by road. Most travellers visit by private car or organised tour from Luxor, commonly combining it with Dendara on the same day.
The trip is long enough that an early start matters. Public transport gets you closer via towns on the Nile rail line, but the last stretch to the site is awkward without a taxi, and security/checkpoint rules can change.