how to read the text in @newwindow if im using /debug @newwindow to open it ?

use that
/debug -i @newwindow zzz
Alias Zzz {
echo -s Debug: $1-
return $1-
}

If you need to scan every line you can use the -i switch as Adrenalin mentioned, but a custom window (or a file) isn't needed at all. Just use /debug -i nul <alias>

"nul" is a special system device to which you can redirect stuff you don't need, and /debug (unlike commands like /write, that claim "nul" isn't a file) allows you to use it.

Cool, I didn't know that (NUL). Too bad things like this aren't documented in the help file.