Kukui- study of Pokemon moves.
Magnolia- the Dynamax phenomenon.
Sonia- Galar's history.
And, if anyone is curious, these are other characters classified as researchers that are not the main 8 Professors:
Other individuals who study Pokémon
Professor Rowan and his assistants at work
Captain Stern, a leading oceanographer from Hoenn's Slateport City.
Professor Cozmo, a meteoriticist of Fallarbor Town.
Fennel of Striaton City, Unova, Professor Juniper's friend who specializes in studying Pokémon Trainers, as well as studying Pokémon dreams.
Cedric Juniper of the Unova region, Professor Juniper's father who used to be a Pokémon researcher. He studies Pokémon distribution and biology.
Samson Oak, Professor Oak's cousin of the Alola region, who studies regional forms and Totem Pokémon.
Professor Andrew Park, who runs the Poké Transfer Lab.
Colress, a researcher who studies Pokémon strength.
Professor Silktree, mentioned in a note on the PC in the Ruins of Alph in Pokémon HeartGold and SoulSilver as the founder of the Research Center.
Bugsy, the Gym Leader of the Azalea Gym, is not only a Bug-type specialist, but also a researcher of Bug-type Pokémon.
Bill, a Pokémon Researcher and expert in many fields.
Kurt, a Apricorn Poké Ball maker who also studies Poké Ball mechanics.
Professor Burnet, who studies the relationship between Pokémon and other dimensions from the Dimensional Research Lab
Mohn, a former professor at the Aether Foundation, and the one who first confirmed the existence of Ultra Wormholes and Ultra Beasts.
Professor Krane of the Orre region, who specializes in the purification of Shadow Pokémon.
Dr. Kaminko of the Orre region, who specializes in the creation of Robo-Pokémon.
Professor P of the unnamed region featured in Pokémon Trozei!, head of SOL, who invented the Trozei Beamer.
Professor Hastings of the Oblivia region, the creator of the Capture Styler used by Pokémon Rangers.
Professor Willow in Pokémon GO, who studies the regional distribution of Pokémon.
Professor Bellis in Pokémon Masters, who studies the relationship between Pokémon and sync stones.
Other fields of study
Dr. Astropoff, a scientist and astrologer.
Professor Quentin Werty in Learn with Pokémon: Typing Adventure.
Professor Andy in Pokémon Art Academy.
Professor Tetra in Pokémon Picross.
Leanne of the Oblivia region, an archaeologist who is studying the connection between the ruins and fairy tales of Oblivia.
In the anime
Other professors, scientists, and researchers introduced in the anime include:
Dr. Fuji, creator of Mewtwo.
Professor Westwood V of the Seafoam Islands, Kanto, a Pokédex programmer.
Professor Ivy of the Orange Archipelago, who studies the regional differences between Pokémon.
Gary Oak of Pallet Town, Kanto, a Pokémon researcher known to have researched Fossil Pokémon, successfully resurrecting a living Aerodactyl and researching the habitat of supposedly extinct Shieldon. He has also shown interest in the Legendary Pokémon of Sinnoh.
Dr. Gordon of Saffron City, Kanto, Pokémon inventions specialist.
Professor Jacuzzi, Gulpin specialist.
Professor Lund of LaRousse City, Hoenn, the leading authority on Deoxys.
Professor Kodama, inventor of the "Affinity enabler".
Dr. Namba, a Team Rocket scientist.
Dr. Wiseman, a researcher of Shiny Pokémon.
Isaiah, studies Clamperl and its pearls.
Marie and Pierre, currently co-writing a research paper on whether Sudowoodo is a Rock-type or a Grass-type.
Naomi, studies communication between Water-type Pokémon, specifically Lapras.
Luna Carson, studies Pokémon habitats from her home in Purity Canyon.
Professor Cerise of the Cerise Institute in Vermilion City, studies Pokémon and their ways of living.
Other fields of Pokémon study
Pokémon computer scientists
Dr. Akihabara, anime-canon creator of the Pokémon Transfer System and Porygon.
Dr. Yung, inventor of the Mirage Pokémon system.
Eve, discoverer of the ancient lost city of Pokémopolis.
Professor Telesu, who was doing research on hieroglyphics near a Slowpoke colony.
Tierra, excavator of an ancient city that was ruled by a queen in Johto.
Professor Hale of Greenfield, Johto, who researched rare and Legendary Pokémon including the Unown.
Professor Alden of Oldale Town, Hoenn, who studied ancient ruins in Hoenn.
Professor Carolina of Celestic Town, Sinnoh, head of the Celestic Town Historical Research Center.
Ferris and Sierra, amateur archaeologists that study Unova's Twist Mountain.
A Nurse Joy of the Orange Archipelago, who led the expedition to Fukuhara Island No. 4.
Dora, who worked with Gary at the Sayda Lab.
Professor Proctor of Wales Island, Hoenn.
Dr. Kenzo of Oreburgh City, Sinnoh, in charge of Oreburgh Museum's Fossil-restoration program.
Foster, discovered the Fossil Pokémon Omanyte and Omastar living at the Ruins of Alph.
Professor Serena of Bomba Island, Hoenn, who teaches at the Pokémon Battle Judge Training Institute
Other fields of study
Professor Icarus of Unova.
Professor Malveaux, heads the Ferroseed Research Institute, which studies moss samples and their properties.
Dr. Anna, operates a clinic and uses her Pokémon to help people's health.
Dr. Proctor, runs a hospital for people.
Bart and Millie, workers at Hoenn's Weather Institute.
Mariah, uses several Hoppip to study wind patterns.
Cullen Calix, studies medicine and works at the Pokémon Institute.
Newton Graceland, interested in the Reverse World and invented several machines to reach the location.
Tonio, studies how energy moves from his lab under Alamos Town's Space-Time Towers.
In the manga
Other professors, scientists, and researchers introduced in the various manga include:
In the Pokémon Adventures manga
Apart from the main Professors of each region, there are also two notable Pokémon researchers: Professor Yanase Berlitz of the Sinnoh region, who researched ways to control Legendary Pokémon such as Rayquaza; and Mr. Berlitz, her husband. Currently, both of them work as Professor Rowan's assistants.