Drawing hand animation - transform by trim paths

Automatic Whiteboard - https://aescripts.com/automatic-whiteboard/ looks useful and it comes with a Trial Version.

The simplified solution (assuming i understand the question) is just copy past the path data to the position of the "hand" layer.  I've attached a very basic video showing how.  Depending on the complexity or number of paths the process may need to be repeated on multiple layers or hold keyframes may need to be inserted into hands animation to make it looka little more like natural writing.   All I'm doing in the video is selecting the path, hitting CTRL C to copy and the CTRL V to paste that info onto the position layer of the hand image.  Then I align the initial keyfram and, selecting alll the keyframes I hold down the ALT key and drag the keyframes out to match the duration of the trim path key frames.  Hope that makes sense

https://vimeo.com/500047429

It should be noted that in the video you provided the hand is not accurately following the drawing.  It's just moving around the areas as they're being revealed and because it's happening quickly it gives a "good enough" illusion that the hand is drawing it on.  The brain sees what it THINKS it shoud be seeing.  This is something to keep in mind when creating visual content, often "close enough" is more than enough because the brain is easily tricked

You can attach layers to paths using rather convoluted and ugly expression code, but unless your "writing" is super smooth that won't do you much good, as it may look terribly choppy and you would need to re-rig it for every separate path segment, anyway. And technically that's not how you write with ink and pen, anyway. Other than that AE has no proper constraints. It's all custom expression code, sometimes packaged into scripts. You may find some useful helpers on AEScripts.com if you feel so inclined, but otherwise an excursion to the online help's expression section might enlighten you.

Mylenium