I suggest starting with "Primer on Biostatistics" by Glantz https://www.amazon.com/Primer-Biostatistics-Seventh-Glantz-P... which contains the basics you need to know to do analysis of stats analysis.

I haven't read it, but you'll probably want a book like https://www.amazon.com/Design-Studies-Medical-Research/dp/04... or https://www.amazon.com/Study-Design-Statistical-Analysis-Cli...

realistically you need at least a master's degree in a quantitative field to get the time and knowledge required to evaluate studies like this. I see a lot of armchair "scientists" trying to evaluate studies, it's very common to see basic mistakes in evaluating papers.