Highlighting touches/gestures on an iPad
As far as I know, doing this in the way you say, seems to be impossible (thats not to say it might not be changed).


I think I've seen something like this in screen-captured videos before, so I think it's possible.

This was almost certainly on an Android device, where there is a system setting to enable visual presses. If only it was also an iOS feature.

What would I do in your situation?
Take advantage of the fact that the iPad is plugged into the Mac, and use the mouse to point out bits you want to emphasise (I'm not entirely sure how Zoom works on Mac/how plugging in the iPad works, but if the cursor doesn't show up, you could try screen sharing your entire desktop not just the ipad screen app)
If that doesn't work for you could try;

Attaching a bluetooth mouse to your iPad and using that to point at anything (works better than the mac if you want to be able to use the mac for other things)
Circling whatever you want to draw attention to, then undo after
Using the assistive touch icon on the screen as a makeshift 'cursor' by dragging it around the screen to where you need it, then letting it go back to the edge when you don't (although its quite big, and will continue to take up space on the screen even when not in use)
Changing applications to something that has a laser pointer tool

Making a blank keynote presentation &gt; opening thee 'more' menu (3 dots in a circle) &gt; rehearse slideshow &gt; annotate (the icon that looks like a pen drawing), will allow you to do basic drawing and pointing, although you might be able to find something else
If you do end up changing apps, check the settings of each app you test, as the devs may have added a touch input setting, (I have seen it in very random apps, although none of them would fit with drawing diagrams)



Hopefully you can get something helpful from this.