Let's assume that you wish to use "ns1.domain.com" and "ns2.domain.com" as DNS servers for all hosted in Plesk domains.
First of all, the nameservers should be resolved by Plesk server, so create "domain.com" domain in Plesk and make sure that "A" and "PTR" Records for the both NSes exist in it's DNS zone:
ns1.domain.com. A 10.10.10.10 ns2.domain.com. A 10.10.10.11 10.10.10.10/ 24 PTR ns1.domain.com. 10.10.10.11/ 24 PTR ns2.domain.com.
(Note, 10.10.10.10 and 10.10.10.11 IPs should bre replaced with the real ones)
Now you should be able to point NSes for the "domain.com" zone to Plesk server by means of Registrar where "domain.com" was registered.
After the action above, you have two nameservers and they point to the Plesk server. Add the appropriate records to the DNS template on the Server > DNS Settings page in Plesk CP, so all new domains use these NSes:
<domain>. NS ns1.domain.com. <domain>. NS ns2.domain.com.