https://app.demiplane.com/nexus/pathfinder2e/character-sheet/71e1441d-d093-43c8-ba02-c6676ebea88e
This is my character. I have assurance in nature. I’m expertly training with a +13. With assurance, my value should be 23. It is listed on my character sheet as 19.
With assurance you only get your proficiency bonus. Expert (+4) + level (+5) + 10 = 19.
Thank you. It makes sense now. I thought it was just as if you rolled a 10 on your dice and then add your skill.
Sadly, no. There’s a fair amount of analysis over at Paizo forums regarding this feat. It’s basically worthless. In your case, with a +4 ability modifier, it’s the same as a take 6, not a take 10. Not to mention that all other bonuses are ignored, too, such as those conveyed by feats or items. It’s just a bad feat.