Because the code is lost, how to read the code burned into RP2350?
Welcome to the forum
Are you hoping to get back the original sketch or the executable code that was uploaded ?
The original sketch is not on the board and hence it cannot be recovered from it. The best that you could hope for would be to download the executable binary code
What is it that you want to do and under what circumstances was the original sketch lost ?
The Raspberry Pi foundation were offering a prize for the first one to be able to do that because they believed it was not possible, because that is the way they designed it to be.
The computer system is broken, and the code is lost after reinstalling the system. 
Thank you. It seems that I can only rewrite it. 
Next time it might be possible to use a Linux live CD or Hiren’s BootCD before re-installing and backup your data. It might also still be possible to recover your source code using recovery tools (e.g. if you used a quick format); the less you use your system before doing so the better your chances.
One of the most important rules when working with a PC: Make regular backups of all important data on an external storage medium.
No backup - no pity in case of data loss 
.
Unfortunately, some people have to learn this the hard way - I hope you've learned your lesson now 
Make sure there is not a windows.old folder, that sometimes gets created when reinstalling windows.
Is this code C/C++ (Arduino) code or Python code?
If it is Python, it will still be on the board, I think. Plug it in to a PC and it should appear as a drive. Open the drive and you will see your .py file.
If it is C/C++, the answers above are correct.