This is the list of families that learn Knock Off in Gen VIII (incl. expected families):
-Machamp, Tentacryel, PJ Fardetch'd, G Farfetch'd, Sirfetch'd, Kingler, Lickitung, Lickilicky, Tangela, Tangrowth, Omastar*, Kabutops*, Shuckle, Ludicolo, Pelipper, Gardevoir, Gallade, Sableye, Crawdaunt, Armaldo*, Drapion, Regigigas*, Swoobat, Crustle, Archeops*, Zoroark, Cinccino, Escavalier, Ferroseed, Ferrothorn, Mienshao, Mandibuzz, Decidueye, Salazzle, Passimian, Rillaboom, Thievul, Centiskorch
Notable Pokemon w/o Knock Off (around 80%, and IIRC all STAB/Relevant Pkmn): Venusaur, Pikachu, J Raichu, A Raichu, J Sandslash, A Sandslash, Clefable, J Persian, K Persian, A Exeggutor, Hitmonlee, Scyther, Scizor, Pinsir, Leafeon, Mew, Azumarill, Heracross, Sneasel, Weavile, Mamoswine, Blaziken*, Absol, Toxicroak, Uxie*, Mesprit*, Azelf*, Liepard, Gurdurr, Conkeldurr, Throh, Sawk, Krookodile, Scrafty, Cofagrigus, Bisharp, Tornadus*, Thundurus*, Landorus*, Diggersby, Pangoro, Malamar, Yveltal*, Incineroar, Mareanie, Toxapex, Lurantis, Tsareena, Passimian, Golisopod, Tapu Fini*, Solgaleo, Nihilego*, Kartana*, Guzzlord*, Necrozma, Marshadow, Zeraora.
*Prediction