@amitesh1505 Welcome to the community 
For array objects you can access using dot notation or bracket notation. When the attribute name contains “.” in it, its advised to use bracket notation in JS. You can find more info here.
Similar thread is discussed here and another one.
Something like the below snippet in your case
response['validationResponsesMap']['individual.name.lastName']['ruleType']
Let us know if you still face any issue here in parsing the response 