Should a graduate student accept random offer to be a reviewer for IEEE Transactions paper? I have been asked by a well-established professor to review a regular paper submitted to IEEE Transactions, however, I am concerned as in the email, he titled me "Dr. Monkia" although I am still being a graduate student. Of course, I am interested in the paper's topic, but I don't consider myself an expert. He asked if I couldn't review, I can ask a qualified colleague to do so, or let him know immediately.

I had been asked many times to review for predatory conferences or journals, of course, I declined. As far as I know, IEEE transactions are reputed, however, this sounds a little bit weird.

The question: as a graduate student should I accept to review or decline in that case (given the fact I know the topic)?
It is probably a good thing to do, just for the experience. It will also get you on the good side of the professor. 

However, make sure, in accepting, that the professor and others know that you haven't finished your degree yet. That might cause them to withdraw the invitation, of course, but it should be made clear.