How can I add a table of contents to a Jupyter / JupyterLab notebook?

You can add a TOC manually with Markdown and HTML. Here’s how I have been adding:

Create TOC at top of Jupyter Notebook:

## TOC:
* [First Bullet Header](#first-bullet)
* [Second Bullet Header](#second-bullet)

Add html anchors throughout body:

## First Bullet Header <a class="anchor" id="first-bullet"></a>

code blocks...

## Second Bullet Header <a class="anchor" id="second-bullet"></a>

code blocks...

It may not be the best approach, but it works. Hope this helps.