Is there any good examples or article to understand Json_value or Json_query flink sql functions?

The best examples can probably be found in the

JsonFunctionsITCase

test from Flink itself, see https://github.com/apache/flink/blob/master/flink-table/flink-table-planner/src/te[…]g/apache/flink/table/planner/functions/JsonFunctionsITCase.java