This snippet goes two ways. You can type /ascii win to create a new window with the characters, or /ascii dial to create a dialog with the characters. Your choice to what you think is easier. Please note this does NOT cover characters below 32. I might update it later though. Thanks in advance for any advice or feedback.

; ascii set (window or dialog)
; eXiled
; /ascii win
; /ascii dial 

dialog asc {
  title "Ascii dialog"
  size -1 -1 168 34
  option dbu
  list 1, 1 5 83 26, size
  box "", 2, 87 2 75 29
  text "Character:", 3, 89 10 28 8
  text "", 4, 119 10 28 8
  text "Asc value: ", 5, 89 19 29 9
  text "", 6, 119 19 28 9
  button "!", 7, 148 9 11 9
  button "!", 8, 148 19 11 8
}

on *:dialog:asc:init:0:ascload dialog
on *:dialog:asc:sclick:*:{ 
  if ($did = 7) clipboard $did($dname,4).text
  if ($did = 8) clipboard $did($dname,1).seltext
  if ($did = 1) { 
    did -ra $dname 4 $asc($did($dname,1).seltext)
    did -ra $dname 6 $did($dname,1).seltext
  }
}
alias ascii { 
  if ($1) { 
    if ($v1 = win) { 
      if ($window(ascii)) window -c @ascii
      window -lk @ascii
      ascload window
    }
    if ($v1 = dial) { 
      dialog $iif($dialog(asc),-v asc asc, -m asc asc)
    }
  }
}

alias -l ascload { 
  if ($1) { 
    if ($v1 = dialog) { 
      if ($dialog(asc)) { 
        var %x 32
        while (%x <= 255) {
          did -a asc 1 $chr(%x) 
          inc %x
        }
      }
    } 
    if ($v1 = window) { 
      var %x 32 
      while (%x <= 255) {
        aline -p @ascii Character $chr(%x) 
        inc %x
      }
    }
  }
}

menu @ascii { 
  dclick:clipboard $gettok($sline($active, 1),2,32)
  Copy Character:clipboard $gettok($sline($active, 1),2,32)
  Copy Ascii Number:clipboard $asc($gettok($sline($active, 1),2,32))
}