Hi @pereirath,
I took both certifications recently, and might be able to give you some hints.
Let's start with the NSO-159. It's an administrator level certification, that require you to have a few months experience administering ONTAP. The questions have been written on ONTAP 9.3.
To best prepare for it, there are some NetAppU trainings available, such as the ONTAP, NFS and SMB Admin trainings. These trainings are Instructor-led, or Virtual.
For the NSO-513, you will need to have experience and knowledge about embedded Data Protection of course (DP, XDP, SVM-DR, etc.) but also SnapCenter. Knowledge of MetroCluster IP and Elements OS to ONTAP SnapMirror are also required.
Finally, you can find all references used to write the questions in that document: https://www.netapp.com/us/media/ncp-reference-document.pdf
I think that can always help prepare.
Good luck!
Ron.