The encyclopedia device used to identify Pokémon is called the Pokédex. In the games and anime, it records information about Pokémon species and helps trainers learn about the creatures they encounter.
The name combines “Pokémon” with “index.” In the original games, the player receives a Pokédex from Professor Oak and is encouraged to document Pokémon by catching them and recording their entries.
The Pokédex is more than a simple list. Depending on the game or animated series, it can provide a Pokémon’s name, type, height, weight, habitat, abilities, and other biological or regional information. Its contents vary between regions and generations.
The PokéNav and Pokégear are different devices from later Pokémon games. They provide navigation, communication, mapping, or other utilities, but they are not the standard encyclopedia for cataloging Pokémon species.