I want to ask about black magic and how to recognize the person who do it?

As Salamu Alaykum,
Here is a good website it has the symptoms of black magic and the explanation of different types of black magic: http://www.blackmagicremoveswithquran.com/
This website is also good:
http://getrideviljinndevilwiththehelpofquran.blogspot.com/
If you want to find out who did black magic on you I would advise you to read 2 naaful namaaz and tahajud and humbly ask Allah swt as to whether someone did black magic on you. You might see it in a dream, but I think you should look at the symptoms to see if any are present. Usually a jealous relative peforms black magic on someone, so you should check to see if anyone envies you.
http://www.slideshare.net/guestb82c387/if-you-wana-know-wether-or-not-you-are-in-black-magic-with-the-help-of-quran
Recite Ayat ul Kursi and the last three verses of the Qur;an, particularly surah falak and naas. Try listening to the qur'an and see if you have any side effects.
InshaAllah, I hope you find out who did black magic on you if you are under one. Just keep on making dhikr and du'a asking Allah swt if your are under a black magic spell.
If you do find out that you are a victim of black magic then I would advice you to go on this website it has lots of information. And if you do experience symptoms and you don't know what procedure to follow then you can post a question for advice.
InshaAllah I hope you are not under s black magic spell, but its better to check. The sooner you find out the better.
Take Care.

Sorry I forgot to mention the last website:
http://islamicexorcism.wordpress.com/category/islamic-exorcism/blackmagic-islamic-exorcism/