Here's the guy who attacked Robert and broke one of his fingers

https://twitter.com/IwriteOK/status/1297270144947765248

He's visible in some high resolution footage elsewhere, like around 0:33 here

If you want to try and find other shots of the guy (at some point, I'm sure he shows his face), look around for footage from these sources:
https://twitter.com/MrOlmos/media 
https://www.youtube.com/results?search_query=portland&sp=EgJAAQ%253D%253D
https://www.youtube.com/results?search_query=portland&sp=CAISBggCEAEgAQ%253D%253D https://map.snapchat.com/@45.515850,-122.678325,17.00z

A few details on the Trump protester who broke @IwriteOK's finger --
Distinct moles / birthmarks on his face
Multiple tattoos on his hand/forearm, including letters on his right hand and a pocket watch on the top of his hand

A few more photos of him, where you can see some obvious details (Trump shirt, GoPro camera, flat-brimmed USA hat with sticker still on, camo face covering, etc)

Good view here that @gianfiorella found, showing his hat says Oregon on the back and he was either recording or streaming throughout. Note tattoos on his left hand/forearm too.
(11:58 )

Full face at 52min and onwards
https://www.facebook.com/pazwell/videos/798245527649653

He's probably a Proud Boy, so if you're interested in helping, look for previous photos/videos of Proud Boys protesting in Portland (e.g. Patriot Prayer)

Super high-res of his hands and phone, via a photo taken by @abrookeherbert
https://www.oregonlive.com/portland/2020/08/downtown-portland-braces-for-opposing-rallies-at-noon-saturday-live-updates.html

Here he is again: https://twitter.com/_WhatRiot/status/1297623468398112769?s=19

We've IDed him, thanks all for the crowdsourcing help!