What should I know if I want to "learn an ontology"?

Hey everyone, got a really hard question here and need an advice. What do I need to know if I want to "learn an ontology" (nlp sense)?

Speaking of my case, the ontology will be used for "enriching unstructured data with knowledge via mapping onto structured ontologies".
My guess regarding the meaning of this is that each (almost) word in a document will be associated with an entity from an ontology as well as there will be some kind of …

languagetechnology ontology