@ManojBhosale
The GraphQL documentation does not exist in a nice, well-structured, web page like the REST API is. Because GraphQL allows you to pull information from many objects with one query, it would be difficult to organize like the REST API documentation does.
You could look at the source code for Canvas' implementation of GraphQL, but it may be overwhelming. For instance, if you look at the assignment_type file, you can see things like post_to_sis that is Boolean, has a description of "present if Sync Grades to SIS feature is enabled" and can be null. But there are a lot of other fields (such as allow_google_docs_submission) that have no description at all.
What I do is add /graphiql [note the extra i between graph and ql] to the end of your main Canvas instance's URL. This brings up an interactive GraphQL explorer that allows you to create queries and mutations. The right side has a documentation explorer. If you go to "assignment" and click on "postToSis" or "allowGoogleDocsSubmission" (underscores have been turned into camelCase), it adds it to your query. If you want to see the documentation for any item in your query, you can hover over it and then click the link to bring it up in the documentation panel on the right.
Using the interactive interface is a lot easier than trying to understand the source files. The documentation on each property is either short or non-existent and there aren't examples of how to use it baked into the documentation like with the REST API.
