//wrapper class
public class JSON2Apex
{
    public Datetime DateModifiedUtc{get; set;}
    public List<AgentInfoList> AgentInfoList{get; set;}
}

public class AgentInfoList
{
    public String Username { get; set; }
    public Integer PriorityNumber { get; set; }
}

public static JSON2Apex parse(String json)
{
    return (JSON2Apex) System.JSON.deserialize(json, JSON2Apex.class);
}

public CalloutAgentList()
{
    info = (JSON2Apex)parse(helloKitty);
    system.debug('this is the string-->' + info);
    system.debug('this is the string-->' + info.AgentInfoList);
    system.debug('this is the string-->' + info.DateModifiedUtc);
    changeToPst = info.DateModifiedUtc;
    System.debug('This is the Converted Time to PST is ' + changeToPst.format('MM/dd/yyyy HH:mm:ss', 'America/Los_Angeles'));
    newDate = changeToPst.format('MM/dd/yyyy hh:mm aa' , 'America/Los_Angeles');
}

static testMethod void testParse() {
    String json = '{"DateModifiedUtc":"2016-09-07T20:12:47.1519119Z","AgentInfoList":[{"Username":"Agent00@gmail.com","PriorityNumber":0},{"Username":"Agent01@gmail.com","PriorityNumber":0},{"Username":"Agent02@gmail.com","PriorityNumber":0},{"Username":"Agent03@gmail.com","PriorityNumber":0},{"Username":"Agent04@gmail.com","PriorityNumber":0},{"Username":"Agent05@gmail.com","PriorityNumber":0}]}';
    JSON2Apex obj = JSON2Apex.parse(json);
    System.assert(obj != null);
}

WrapperClassName.JSON2Apex obj = WrapperClassName.JSON2Apex.parse(json);

public MyClass
{
    public class JSON2Apex
    {
        //...
    }
    //...
    static JSON2Apex parse(String input)
    {
        //...
    }
}