NS questions.

[Okka DNS]

I have a domain.

Example.com.

                NS      ns0.dns.tld.
                NS      ns2.dns.tld.

                MX      5 mx.dns.tld.

mail            A       1.2.3.4

subdomain  A       1.2.3.5
$ORIGIN subdomain.example.com.
;                NS      ns0.dns.tld.
;                NS      ns2.dns.tld.
                 MX      5 mx.subdomain.tld.

If I do dig ns example.com then I get an answer that states that ns0.dns.tld
and ns2.dns.tld are authorative.
How do I set up my zone file so that if I do dig ns subdomain.example.com
that it answers by saying that ns0.dns.tld and ns2.dns.tld are authorative.
With the entries commented out , the MX for subdomain.example.com works when
doing a dig mx subdomain.example.com but when I uncomment the NS entries for
subdomain , then the NS records for it and the MX records for it does'nt
work.
Is it possible ?