Glue records for sub domains?

Let's say I own example.com

I created an A record called dns.example.com then point it at a nameserver.
On the nameserver I gave it the name ns1.dns.example.com and also dns.example.com

Now I'm confused. Do I create glue records of ns1.dns.example.com or dns.example.com? Do I also still need the A records for my dns.example.com?

Answer

You need glue records if the NS records for a domain point to hostnames within that domain. For example, this would not need glue-records:

testing.example.com:
NS = ns1.infra.example.com.
NS = ns2.infra.example.com.

Where, this one would need glue-records:

testing.example.com:
NS = ns1.testing.example.com.

NS = ns2.testing.example.com.

In that case, the glue records go into the example.com domain.

example.com:
[...]
testing.example.com.     IN NS ns1.testing.example.com.
testing.example.com.     IN NS ns2.testing.example.com.
ns1.testing.example.com. IN  A 172.16.202.152

ns2.testing.example.com. IN  A 172.12.9.11