I haven't found any tools that would do that automatically, though there are websites that can help show you vanilla JavaScript equivalents to jQuery functions and common tasks. I refer to both of these just for a good JavaScript reference on how to do things even when I'm not working with jQuery code:

• You Might not Need jQuery: youmightnotneedjquery.com
• Ditching jQuery: gomakethings.com/ditching-jquery

This really isn't something I would trust any "tool" to do for you; but to be fair I don't trust anyone who would use jquery by choice to write sane or competent JavaScript in the first place! That is why as I'm always saying EVERYTHING I've ever seen done with jQuery falls into one of three categories:

1) Stuff that would be as much or even less code without jQuery - NOT counting the size of the framework against that total.

2) Stuff that's HTML or CSS' job and has ZERO damned business in the scripting.

3) Stuff that has ZERO damned business on a WEBSITE in the first bloody place if you care about speed, accessibility, usability, or sustainability.

First question I'd be asking is "does the page work with scripting disabled or blocked?" -- if the answer is no, then you've got far deeper rooted problems than what some joker slopped together in the train wreck of how NOT to build a website that is jQuery!