How to import functions node.js

You should have this:

const AWS = require('aws-sdk');

in any module that wants to use this AWS SDK. The module system uses a cache so the module itself will only be loaded once (the first time it is required) and from then after will just return the same exports object that was originally loaded.

The rest of your question is not entirely clear as there's no AWS2 object in any of your code that you show so it's unclear what you think you have two of. If you're just talking about the monkey-dynamodb-functions.js file, then yes, it must also require in the AWS module so it can use it.

Unlike in the browser, each of your nodejs files runs in its own module. So, when you do something like this:

const AWS = require('aws-sdk');

in the main file, that AWS symbol is local to only this module. It cannot be accessed directly by any other module. So, in any other module that you also want to use the AWS sdk, just require it into that module also.

You can share objects or functions from one module to others by exporting them from one module and then requiring them into another module from that module and every module that wishes to have access to that shared object would require it in separately. That's what the aws-sdk module is itself doing.

but the compiled code still creates multiple AWS objects

It's not entirely clear what you mean by this. If you mean that when do require in the aws-sdk in both modules, you will then have two separate variables for the AWS sdk, that is true. That is the correct way to program it. Each module contains its own set of local variables. Those two variables will each contain the exact same aws-sdk object reference. This is the correct way to code with modules in nodejs.

Main file

const AWS = require('aws-sdk');
const monkeyDynamodb = require("../includes/dynamodb/monkey-dynamodb-functions.js")
...
exports.handler = async function(event, context) {
    let billingDevices = monkeyDynamodb.scan("SensorNodeBilling");
    ....

monkey-dynamodb-functions.js

const AWS = require('aws-sdk');

async function scan(dbName) {
    var docClient = new AWS.DynamoDB.DocumentClient();
    ...
}

exports.scan = scan;