I have a question about how stub zones work, or more specifically, is there
a controlled way in which a query gets forwarded to certain NS server from
the list of NS records in the stub zone? or does the query get sent to a
random NS server that the DNS server decides to send it to?

Scenario:

zones: ad.local; zone2.local

DNS servers:

DNSserver1.ad.local
DNSserver2.ad.local

DNSserver1.stub.local
DNSserver2.stub.local

Servers "1" for each domain are in SITE 1.
Servers "2" for each domain are in SITE2.

If I setup an ADI stub zone for stub.local on the ad.local DNS servers, and
then a client in SITE1 queries the ad.local servers for that stub.local
zone, which DNS server is the stub.local zone will the query get forwarded
to? Will AD sites and services determine if a server in your same subnet or
AD site will respond or will you get forwarded to a random NS server for
that zone?

I've looked through MS documentation and can't find anything that talks
about how that actually works. Any assistance would be appreciated. If I
haven't been clear, let me know and I'll try to explain better what I'm
trying to find out. Thanks.