If you seek recent information, New Bark Town and Pallet both have laboratories. For history your best bet would be Ecruteak, with Pewter's museum a close second. Relevant items and books are easier to find in Goldenrod's and Celadon's Department Stores, but you can find minimal information in every town. ...Of course, the Pokémon themselves can be observed anywhere, with a particularly high number of species to be found in the Safari Zone.