First of all, if you are talking about the official certification, I must tell you that such a certification is not provided by NodeJs. So, in general, if you want to have a certificate in NodeJs, then you have two options: either join an online NodeJs Training Course or find out any offline NodeJs course. However, I would suggest you learn it online.
There are many reasons why you should enroll in an online training course:
You save a lot of time that you can spend in further study.
You can access your course material at any time.
You get 24/7 support to solve your queries, which you can not get in offline training.
You can also avail of a 1:1 mentorship during the course; whereas in offline training, mostly, one trainer deals with the whole batch.
It looks like you are a beginner. So, first, watch the following video tutorial to begin with NodeJs: