Knowledge graph is showing the information you are search for in the real world like person, movie, book, company.
when you have a question, others may want the same answers on the basis of all collective human wisdom that comes through google search.
How to get a knowledge graph:
1. Create a google Plus account and claim your listing (plus.google.com)
2. Get listed in Freebase, Wikipedia and Wikidata.(freebase.com)
3. Use Structured data (Schema.org) – website listing
Article on how to get on Google Knowledge Graph.
schema is like a code which tells google where to find the results from.