Hi!
Unfortunately, node-powershell isn’t going to work with Observable - it’s a module that runs only in Node.js and as part of a server or on the command-line. Observable is a web environment and runs code on the web in browsers - so it won’t have Node.js built-in modules like spawn or the ability that that module has to spawn processes.
Like other web apps, Observable won’t be able to access your local data by a script alone - which is a good thing, because if it did, websites would gleefully steal your data 
To load data, check out Mike’s Introduction to Data notebook - which shows how to upload data to the web and load it in a notebook - and check out the DOM.input(‘file’) method in the standard library notebook, which lets you add a file input to a notebook and read the results.