D3 is not rendering in CEWP (SP2013)

@Denis Molodtsov is right, you need to add ID to your DIV tag to make it unique.

Below is my test result in SharePoint 2013：

<script src="https://code.jquery.com/jquery-3.5.1.min.js"></script> 

<script src="https://d3js.org/d3.v6.min.js"></script>

<style>

    .container{
        width: 250px;
        height: 200px;
        display: flex;
        justify-content: space-around;
    }
    .bar{ background-color: #720570;}
</style>

<div id="test"></div>

<script>
$(document).ready(function () {

    test();
});

function test()
{
    const DummyData=
    [
        {id:'d1', value:10,region:'USA'},
        {id:'d2', value:20,region:'China'},
        {id:'d3', value:30,region:'Russia'},
        {id:'d4', value:40,region:'Germany'}
    ];

     console.log(d3);
     console.log(DummyData);
    
    const container=d3.select('div#test')
        .classed('container',true)
        .style('border','10px solid red');

    const bars=container
    .selectAll('.bar')
    .data(DummyData)
    .enter()
    .append('div')
    .classed('bar',true)
    .style('width','50px')
    .style('height','150px');
 
}
</script>

If all scripts were loaded correctly, then the issue is most likely with the selector.

The following CSS-selector will look for the very first DIV in your page:

d3.select('div')

This is definitely not what you need. To avoid selecting wrong divs, you need to add an ID to the DIV you target:

<div id="MyDiv"></div>

Then, modify the CSS-selector to target your DIV like so:

 const container=d3.select('div#MyDiv')
        .classed('container',true)
        .style('border','10px solid red');

There is one more potential problem with another CSS selector:

const bars=container.selectAll('.bar')

In the code above you are trying to select an elemnt with a bar class, but I don't see it anywhere in your code. I'm not an expert in D3, but maybe you need to create another HTML element with this class?

More info on d3.select()

The d3.select() method returns the first element in the HTML document based on specified css-elector.