I see that knowitian.com is taken, so I assume you bought it. If so, that is your domain name.
But to use it appropriately you need to have it pointed at the forum on Nabble's servers. This is NOT my area of expertise, but my domain name has this entry: CNAME forum s1.nabble.com. That points my domain, garysgaragemahal.com, to the Nabble S1 server.
Then, on my forum under Options/Embedding Options I have it set up as below. Is yours set up to redirect to your domain name? If so, and if you have the domain name pointed at S1 via a CNAME entry then you should be good to go.
But if/when Israel enables https I think you'll need to change the embed code to be https.