I put together a New Video at the Classic_DM YouTube Channel, discussing Proficiency Bonus in Pathfinder Second Edition, citing page numbers from the Core Rulebook for your reference and as a basis for the conversation. Proficiency gives you a bonus that’s added when determining the following modifiers and statistics: AC, Attack Rolls, Perception, Saving Throws, Skills, and the Effectiveness of Spells.
You can follow along with all the source citations here on my Pathfinder 2nd Edition Page
Get your copy of the Core Rulebook at the Official Paizo Pathfinder Page
Pathfinder Core Rulebook (Second Edition) © 2019, Paizo Inc.; Designers: Logan Bonner, Jason Bulmahn,Stephen Radney-MacFarland, and Mark Seifter.