We notice  CIS is issuing lot of queries throughout the day for checking the connection. Is there a way to disable this.
 
The CIS data source we want to disable this is the cache database target. For every query this SELECT 1 query gets invoked when getting connections from the pool.
 
Cache Database used - Vertica/or Any other DB 
Connection Validation Query - SELECT 1
 
Question
1) how to disable this connection validation query feature.
2) what happens of we remove this in the data source advanced tab. CIS/TDV  did allow to save the data source. Just making sure if this will yield the expected outcome of bypassing or not doing the connection validation query
 

How to disable this connection validation query feature?

1) There is no global setting to disable the validation query. However you can disable by removing the query  from the Connection Validation Query under Advance tab of Configuration tab.
2) This is optional field and CIS will allow you to create a DB connection  .However it is recommended from CIS perspective . 
Below is more information from CIS user guide for your reference.
A data-source-specific query that the CIS query engine sends to see if the data source connection is valid. This query is executed every time a connection is checked out from the pool. Enter a query that returns quickly.
If this query returns a non-error result, the data source connection is considered valid. If this query fails, the connection is discarded and a new connection is checked out from the available pool.
No one SELECT statement works with all data sources. To verify that CIS is running and that it can connect to the data source, devise a query against a published table from that data source.