can i use the RESET button on nano as a pushbutton?

Hi,

I'm new here.

how can I use the RESET button on the board as a pushbutton that can be read by digitalRead()
or analogRead() ????

I need only one pushbutton for my project,

so I thought why not just using the one builtin on board?

No, not unless you are prepared to vandalise your board, risk damaging it and are willing to lose the reset button functionality

For quick and dirty testing I use a wire from an Ardiono pin to GND as a switch

You can play tricks to determine if a Reset was caused by the Reset button being pushed, if it came from low voltage (brown out), or some other things.
You could also use the reset signal to latch in a level on some external device, then use digitalRead() to check the latched level and clear it back to the non-latched level after the reset cleared.
That would probably work best if you did not use the bootloader so the program restarted nearly instantly (as compared to the bootloader trying to talk to the PC for a while first) and if you stored and could recover the state of your program quickly so as a user you wouldn't be too annoyed by the reset occurring.