There is a broken link to a article in the below Trailhead trail 

Trail : Prepare for your Salesforce Omnistudio Developer Certification

Link : https://trailhead.salesforce.com/content/learn/trails/prepare-for-your-salesforce-omnistudio-developer-certification

In the first section : Learn Omnistudio Fundamentals 

There is a link to the article "Omnistudio Permission Sets" 

The above link is broken and redirect to a blank page