Is this sentence below incorrect or unnatural?
The professor asked me if I brought my research paper or not.
Mostly, I have used "wheter" with "or not" but I'm wondering if I can use "if" instead of "whether".
Thanks in advance.
As an NES but not a teacher, the following work for me:
The professor asked me if I had brought my research paper with me.
The professor asked me whether or not I had brought my research paper [with me].
The professor asked me whether I had brought my research paper or not.
I noticed a typo in your spelling of whether.
Whatever you do, beware of spelling "whether" as "wether"!
wether - definition of wether by the Free Online Dictionary, Thesaurus and Encyclopedia.