If you cross two parents that that area aa and aa, then self pollinate one of their f1 offspring what is expected genotypic ratio of the f2 population

In your problem, you didn’t put who among the parents have dominant or recessive trait, but if both parents have recessive trait, which you said (aa) and (aa), even if they will self pollinate and even no matter how you cross them, the genotypic ratio would still be aa, aa, aa, aa.