I have a parallel task and inside it can user ask for more information from the requester , I want to ask how can do this inside state machine?
Could you provide more information please? Maybe show a diagram of your state machine. For a start though, you will know who the requestor is because you've probably saved this information somewhere (e.g. created by). Therefore you'll be able to retrieve that item property in your workflow.
If you want more information, you can use the to-do task/flexi-task/request data actions.
Without knowing more information, the only other piece of advice I can give is the state machine executes one branch/state at a time. You can't have two running in parallel. If you need to do this, you use the parallel action which you might be doing already.
You can incorporate the more information Request into the state machine as another state branch. I have used this many times. At the end of the Request action branch, you just send the workflow on its way to whatever the next action should be.