DKIM implementation -- a few questions

I am burrowing into the process of learning how to implement DKIM. I've discovered the set up within Mailwizz's Domains function (at the backend) and also figured out to build DKIM domain keys here

As well, I've figured how to load the relevant text files on the server.

However, there are a few questions:

1. Do I set the domain for DKIM of the nameserver (in my case or do I set i for the "sending domain" ie,

2. The socketlabs generation wizard generates a public as well as private key. It seems that Mailwizz also generates a public? key -- do I use one or the other, or both (with separate TXT entries)

3. if the domain that needs to be associated with the DKIM is the dns nameserver domain, do I need to set up two DKIMs, one for NS1. and the other for NS.2

DKIM you need to setup for your domain only and your sending domain you want to use.

Mailwizz have DKIM generate feature, so you can use that feature and add that key to your DNS.