How do ibidentify the wire of an extension cord two wires?

It depends on the extension cord but I will give you 2 ways and they are each very simple.

On a residential type (what I call a house burner) extension cord with just 2 conductors, you will find that the jacket of one wire is smooth and the other one has ridges. The one with ridges is your neutral or white conductor.

On a more commercial type extension cord with conductors covered by a protective jacket, your conductors in the cord will be color-coded, with black being hot, white being neutral and green or bare being ground.