Debit and credit note issue

Yes then only you can confirm whether they reversed ITC which already availed in Original invoice

It's not mandatory under GST.

But, As per accounting standards the Credit note will be accountable as Debit note in Buyers account...

So, No question required.

Yes it's not mandatory ... as the Mr. Raja Ji reply.
Any way it's going to reflect in CNT/DNT section of 2A , the Recepient is liable to reverse it's ITC .

Yes it is mandatory as far as the parties Books of A/c is concerned .for every CNT of one party , there must be a DNT must be recorded by the other party. Then only the current closing balance of both the parties must be equalised.

Rajasir is right that it is not mandatory asper GST Rule is concerned.