Polygenic Risk Score Plot

I have a dataset of about 6000 people, Chromosome 21. I calculated PRS using plink and PRSice. The plot is shown above. I have two questions regarding this.

1. R2 on the y-axis explains the phenotype variation, but I want another measure like AUC (area under the curve) for comparison with other tools.
2. What these highlighted values (1,2,3 )are representing?