Open pisition in F&O against delivery

How to see which position is open in F&O against delivery. I recd nail from zerodha.
My positions tab is not showing such entry.

If you have positions in Stock F&O, upon expiry those will be physically settled. You can learn more about physical settlement here.

But how to know which contract ?

You can refer to the underlying price and check which Option is ITM.

Not clear yet. I hav 3 puts of niftt anf b nufty snd one put of ultratec c3ment.
Nothing else. Please give example.

Index F&O as cash settled. You’re holding Put Option of Ultratech Cement, which, if expired ITM will be physically settled.

Ihavput of 6000. Stock is at 6300. What would happen now ?

Likely it’ll expire Out of the Money, in that case there will be no physical settlement.

For your 6000 Put Option to expire ITM, the underlying will have to close < 6000.

Would suggest you read this module on Varsity to learn about Options trading in detail.