Most Nile cruise ships offer Wi-Fi somewhere on board — typically the lounge, reception, or dining areas, and increasingly cabins on newer or higher-end vessels — usually included in the cruise price rather than charged separately, though this varies by ship.
Why the connection isn't always reliable
Signal strength depends on cellular network coverage along the river rather than a fixed connection, since the ship itself is moving — don't expect hotel-grade Wi-Fi, especially while sailing rather than moored.
A local Egyptian SIM card with a data plan is a reliable backup for travelers who want consistent connectivity; see Do You Need a Local SIM Card for Your Egypt Trip? for how easy that is to set up on arrival.