hey i'm not an accountant so i want to make sure i do this correctly: discount item for 15% restocking fee that i plan to use for vendor returns. What account should I use?

You should confirm that with the controller or CFO at your company. It will be an Income account of some type most likely, but there can be other scenarios that come into play.

I'm going to go to my controller with this but I just wanted to be a little more educated before i proposed using a discount item to reflect restock fee. I was going to suggest COGS but like I said, i really have no idea what I'm talking about when it comes to accounting

Well, not sure it's my place to say, but if you're a NetSuite Administrator, then I would not expect you to know much accounting at all, and I'd just tell your Controller that if they for some reason think you are knowledgeable in accounting.