Is it self plagirism if i use the same assignent twice in the same course?
The more important question is whether this would be accepted by your professor. If you cite the earlier work it isn't plagiarism and you put the professor on notice about what you've done. But it would be much better (safer) to get permission first. 

Whether it is technically self plagiarism or not depends a bit on whether you have, in some sense, published the earlier work. Probably you have, just by giving it to your professor. But even if it doesn't meet the technical definition, the professor could still penalize you for it. 

And it isn't just the issue of copy/paste of the same words. Even paraphrasing without citation is considered plagiarism if the definition applies. 

I'd guess the professor is already aware of the situation and will have a ready answer for you. They may want you to go deeper into the subject than in the first assignment.