To see which queries are run on your behalf on the MySQL instances when you execute a query on vtgate, you can use explain format=vtexplain. It returns an output similar to what the command line application vtexplain returns - a list of the queries that have been run on MySQL, and against which shards they were issued.
Unlike normal EXPLAIN queries, format=vtexplain actually runs your query, and logs the interactions with the tablets.
After running your query using this extra logging, the result you get is a table with all the interactions listed.
The normal behaviour for EXPLAIN is to not actually run the query - it usually only plans the query and presents the produced plan.
Since explain format=vtexplain really runs your queries, you need to add a query directive to show that you are aware that your DML will actually run.