As per your query,
Registration of will is not mandatory, as under the Indian Succession Act, 1925, it’s considered to be a personal choice of the testator. However, it is advisable to register it, if its contents are to be abided by after the person’s death. Registration of the will happens at the office of the sub-registrar. One must submit address proof, photographs, and witnesses to sign the will.
At the time of registration, you have to submit address proof. If you can provide address proof of Delhi, then you can register the will there.
Hope it helps,
Regards,
Srishti