Skipping past any details of error-checking etc, you could write:
tell application "System Events"
set procKME to first application process where name = "Keyboard Maestro Engine"
tell front window of procKME to return {title, position, size}
end tell
or
tell application "System Events"
set procKME to first application process where name = "Keyboard Maestro Engine"
set lst to {}
set lstWins to windows of procKME
repeat with oWin in lstWins
set end of lst to {title, position, size} of oWin
end repeat
return lst
end tell