If suppose , the time for zuhr starts at 12.02 then am I supposed to offer nafl first? And is it the same for all other prayers that we are supposed to offer the nafl at first except for isha namaz? And I wanted to know if we can offer the nafl for asr prayer after the wajib namaz?

Yes first pray nafela dhuhr then dhuhr prayer then you can offer nafela e Asr followed by Asr prayer