There is a great trail called 'Learn How Tableau Works' - I'd like a few colleagues (e.g. Core SEs) to be able to complete it too. However, it is 'Private' and they cannot see it ?

Hi Alex!

If the trail is under the /content/employee/ path and marked Private

, it’s likely restricted to a specific Salesforce employee audience rather than being a trail that an individual user can make publicly accessible. 

I’d check whether the trail has an internal sharing/audience setting that the trail owner or Salesforce learning administrator can modify. If your colleagues are Salesforce employees but still can’t access it, their Trailhead/employee permissions or audience eligibility may need to be checked. 

If there’s no option to change the audience from the Trailhead side, this would likely need to be handled by the Salesforce/Trailhead team rather than by the individual trail owner.