For e.g. I am creating a site with 2 clients and 1 DC in it. I am setting the subnet to cover these objects. So my site say SITE1 will have 2 clients and 1 DC. So when one of these clients tries to contact DC it will contact DC1 since it is the closest one in its site.
My question is if DC1 and all the 2 clients are from a domain say testing1.com is it possible to include another client and DC from another domain say testing2.com ??
If so, how does the replication occur?
Sites are per-forest. So if the domain in question is in the same forest as the new domain in question, then it would use the same sites.
If it's a different forest, you'd have to set up a whole new Sites and Services architecture.
And, for what it's worth, Microsoft (and most everyone else) basically don't recommend the use of child domains anymore, except in a couple distinct circumstances... so you probably shouldn't be setting up a child domain, nor for that matter does it seem to make very much sense to have two testing domains/forests, based on your question.
