I am having a problem with running FLUKA. when I type in the command fluka in Ubuntu WSL, it display STOP CHINPF.

Dear @ufahmad,

You are not supposed to run fluka (i.e. type “fluka”) directly in the terminal. You should run it through flair.
Did you trying using flair as command in the terminal?

I hope you cd well to where your input file is through cd /mnt/c/folder name and run from that end.