Good question, and something I struggled with as well, as the documentation on this topic is not very clear.
To create a geopoint, create a string column of the format {lat},{lon} where {lat} and {lon} are latitude and longitude respectively. Then you should be able to define a property of type Geopoint in your ontology.
Let me know if this works for you and if you have any questions.
With kindest regards
The ontology manager expects an Ontology Geopoint, which is different from the regular Geopoint in Pipeline Builder. After constructing the Geopoint property, you’ll need to transform it into an Ontology Geopoint.