It's difficult to known what the issue is exactly from this image, if you could explain it in more detail I may be able offer further advice. In the mean time you should read this tutorial: https://www.marmoset.co/posts/toolbag-baking-tutorial/
Top left circle: This is likely because you have hard edges set on the low poly, but have not split your UVs in this area. Top center: It's hard to say here, perhaps some sort of UV issue, or intersection issue? Are you using bake groups to prevent ray intersection? Bottom center: Ray distance error perhaps? Double check…