One of your good employees is not performing well recently and he's usually late, do you punish him or do you try to speak to him and try to help him?

Within the permissible limits allow him to resolve his personal issues with some relaxations but not on a continuous basis.

If the employee is performing good and having great followup with there work and also completing all task as per given time then we have to little bit flexible for time although there is very necessary requirement of punctuality then i will try to resolve the issue of coming late instead of punishment. 

Punishment will be given to all those employees who are purposefully used to come late even they are performing very well. . 

Will try to talk to him to know the problem and try to help him to sort out his problm.

Speak to that person in private and try to understand why his performance is slipping. May be there is is some personal issue at home effecting his\\her professional life.It may be a temporary thing and there is no need to Punish. We all go through some low phase in our lives.This where we need to build a trusting relationship so that employee will open up and say something and express his true feelings.

First go for the talk, ask that employee to find the issue, explain the policy and issues due to his absence and follow the discipline. Punishment is a  last resort.

i think you must find out the reason first and thn accept decicions

You should never punish in the first instance. It is important to try to get to the route of the issue, to find out if the employer can help in any way.

As a Manager, I will talk with him or her what is his or her problem and try to help him or her to solve the problem.

Thanks for your invitation !

Sure ! I will speak with him to know the reason of the same and try to get rid of his problem / difficulties.