According to the UiPath documentation, making an ML Skill public allows it to be accessible via an endpoint from outside of UiPath environment. This means that you can call it without the need to go through a robot connected to the specific tenant1. To do that, you need to select Modify current deployment in the ML Skill Details page > Update skill window, and enable the Public skill option. This will generate an API Key and URL that you can use to connect to the ML Skill from a different tenant1.
Reference:
AI Center - Managing ML Skills
What are the steps in moving a ML Skill to a new Tenant?
AI Center ML Skill export question
UiPath tenant move for AI Center