As first correction I'd not recycle the XHR object from the outer loop in the inner loop.

When you say xmlhttp.onreadystatechange = function() ... in the inner loop, the xmlhttp is already in the readystate, obtained in the outer loop.

So, without further checking what is going on, I'd use two XHR objects (maybe like outerXmlhttp and innerXmlhttp). I'd also recreate the inner XHR for every cycle with:

var innerXmlhttp;

at the top of the outer closure.

Then, inside the cycle do:

innerXmlhttp = new XMLHttpRequest();

This is because of variable hoisting. If you just do this:

var innerXmlhttp = new XMLHttpRequest();

inside the cycle you may get a different behaviour. Just don't do it and write what you mean (hoist variables and assign them where you actually need it).

If all of this isn't enough ask a new, more precise question about what is going on.

This is your code with the corrections:

var outerXmlhttp = new XMLHttpRequest();
var url = "https://wjko5k6250.execute-api.us-east-2.amazonaws.com/motorcycle"; 
outerXmlhttp.onreadystatechange = function() {
  var innerXmlhttp;

  if (this.readyState == 4 && this.status == 200) {
   var allmot = JSON.parse(this.responseText);
   console.log(allmot);
    for(var i = 0, len = allmot.Items.length; i < len; i++)
    {
      id=allmot.Items[i].id
      var url1 = "https://wjko5k6250.execute-api.us-east-2.amazonaws.com/motorcycle/"+id; 
      console.log(url1);

      innerXmlhttp = new XMLHttpRequest();
      innerXmlhttp.onreadystatechange = function() {
        if (this.readyState == 4 && this.status == 200) {
          var myArr = JSON.parse(this.responseText);
          console.log(myArr);
          document.getElementById("img").src = myArr.Item.image;
          document.getElementById("brd").innerHTML = myArr.Item.brand;  
        }
      };
      innerXmlhttp.open("GET", url1, true);
      innerXmlhttp.send();
    }
  }
};
outerXmlhttp.open("GET", url, true);
outerXmlhttp.send();

EDIT: @Teemu's eagle eye

As @Teemu points out in his comment, if you reassign values over and over to the same DOM objects like this:

document.getElementById("img").src = myArr.Item.image;
document.getElementById("brd").innerHTML = myArr.Item.brand;  

you're clearly overwriting whatever value was there before. Instead, you should create and append those DOM objects, more like this:

var img = document.createElement("img");
img.src = myArr.Item.image;
var brd = document.createElement("p");
brd.innerText = myArr.Item.brand;
document.getElementById("motlist").append(img);
document.getElementById("motlist").append(brd);

Obviously, you'll need a <div id="motlist"></div> element or some other parent in the DOM to which to append the new elements.

For paging you may also want to clear those elements in the list... but here we're going overboard.