How to make wordpress visual composer attribute check box checked initially

Solution:

Check the Custom checkbox attribute.

Actually, configuration is possible by array key:

'std' => '', // default unchecked

So you can play with this attribute std with values true/false/'yes'.. and you will see how it changes.

In your case:

"value" => array('key' => 'value' ),

So if 'std'=>'value' your checkbox will be checked.